Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $62.95   12.709%   $70.9503   $70.95   $70.95   $71.00  
  Purchase #2 $106.81   12.152%   $119.7896   $119.79   $119.80   $119.80  
  Purchase #3 $121.62   7.267%   $130.4581   $130.46   $130.45   $130.50  
  Purchase #4 $86.46   4.791%   $90.6023   $90.60   $90.60   $90.60  
  Purchase #5 $155.90   9.558%   $170.8009   $170.80   $170.80   $170.80  
  Purchase #6 $221.49   11.281%   $246.4763   $246.48   $246.50   $246.50  
  Purchase #7 $101.99   12.764%   $115.008   $115.01   $115.00   $115.00  
  7 purchase totals = $857.22       $944.0855   $944.09   $944.10   $944.20