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 $58.94   13.282%   $66.7684   $66.77   $66.75   $66.80  
  Purchase #2 $86.68   6.751%   $92.5318   $92.53   $92.55   $92.50  
  Purchase #3 $212.75   11.279%   $236.7461   $236.75   $236.75   $236.70  
  Purchase #4 $37.75   10.586%   $41.7462   $41.75   $41.75   $41.70  
  Purchase #5 $35.27   7.327%   $37.8542   $37.85   $37.85   $37.90  
  Purchase #6 $237.39   8.707%   $258.0595   $258.06   $258.05   $258.10  
  Purchase #7 $202.72   13.565%   $230.219   $230.22   $230.20   $230.20  
  7 purchase totals = $871.50       $963.9252   $963.93   $963.90   $963.90