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 $113.65   10.673%   $125.7799   $125.78   $125.80   $125.80  
  Purchase #2 $120.99   12.799%   $136.4755   $136.48   $136.50   $136.50  
  Purchase #3 $145.33   13.823%   $165.419   $165.42   $165.40   $165.40  
  Purchase #4 $62.52   11.380%   $69.6348   $69.63   $69.65   $69.60  
  Purchase #5 $143.71   6.381%   $152.8801   $152.88   $152.90   $152.90  
  Purchase #6 $203.35   5.642%   $214.823   $214.82   $214.80   $214.80  
  Purchase #7 $89.82   6.398%   $95.5667   $95.57   $95.55   $95.60  
  7 purchase totals = $879.37       $960.5790   $960.58   $960.60   $960.60