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 $13.81   13.326%   $15.6503   $15.65   $15.65   $15.70  
  Purchase #2 $167.94   9.164%   $183.33   $183.33   $183.35   $183.30  
  Purchase #3 $53.71   3.613%   $55.6505   $55.65   $55.65   $55.70  
  Purchase #4 $119.41   3.771%   $123.913   $123.91   $123.90   $123.90  
  Purchase #5 $148.78   11.326%   $165.6308   $165.63   $165.65   $165.60  
  Purchase #6 $9.63   7.151%   $10.3186   $10.32   $10.30   $10.30  
  Purchase #7 $212.65   6.382%   $226.2213   $226.22   $226.20   $226.20  
  7 purchase totals = $725.93       $780.7145   $780.71   $780.70   $780.70