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 $246.62   8.206%   $266.8576   $266.86   $266.85   $266.90  
  Purchase #2 $144.93   13.570%   $164.597   $164.60   $164.60   $164.60  
  Purchase #3 $18.47   6.821%   $19.7298   $19.73   $19.75   $19.70  
  Purchase #4 $216.79   3.484%   $224.343   $224.34   $224.35   $224.30  
  Purchase #5 $159.61   8.619%   $173.3668   $173.37   $173.35   $173.40  
  Purchase #6 $82.52   11.679%   $92.1575   $92.16   $92.15   $92.20  
  Purchase #7 $21.29   13.326%   $24.1271   $24.13   $24.15   $24.10  
  7 purchase totals = $890.23       $965.1788   $965.19   $965.20   $965.20