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 $74.57   10.679%   $82.5333   $82.53   $82.55   $82.50  
  Purchase #2 $69.40   7.554%   $74.6425   $74.64   $74.65   $74.60  
  Purchase #3 $20.54   11.414%   $22.8844   $22.88   $22.90   $22.90  
  Purchase #4 $174.26   4.809%   $182.6402   $182.64   $182.65   $182.60  
  Purchase #5 $184.93   3.585%   $191.5597   $191.56   $191.55   $191.60  
  Purchase #6 $129.26   3.568%   $133.872   $133.87   $133.85   $133.90  
  Purchase #7 $86.35   9.861%   $94.865   $94.87   $94.85   $94.90  
  7 purchase totals = $739.31       $782.9971   $782.99   $783.00   $783.00