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 $9.25   12.508%   $10.407   $10.41   $10.40   $10.40  
  Purchase #2 $139.39   12.684%   $157.0702   $157.07   $157.05   $157.10  
  Purchase #3 $237.59   3.731%   $246.4545   $246.45   $246.45   $246.50  
  Purchase #4 $102.34   12.544%   $115.1775   $115.18   $115.20   $115.20  
  Purchase #5 $186.39   7.219%   $199.8455   $199.85   $199.85   $199.80  
  Purchase #6 $10.95   9.212%   $11.9587   $11.96   $11.95   $12.00  
  Purchase #7 $199.66   5.505%   $210.6513   $210.65   $210.65   $210.70  
  7 purchase totals = $885.57       $951.5647   $951.57   $951.55   $951.70