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 $224.82   3.470%   $232.6213   $232.62   $232.60   $232.60  
  Purchase #2 $24.92   4.790%   $26.1137   $26.11   $26.10   $26.10  
  Purchase #3 $137.86   10.663%   $152.56   $152.56   $152.55   $152.60  
  Purchase #4 $10.53   3.470%   $10.8954   $10.90   $10.90   $10.90  
  Purchase #5 $169.34   10.669%   $187.4069   $187.41   $187.40   $187.40  
  Purchase #6 $109.94   11.459%   $122.538   $122.54   $122.55   $122.50  
  Purchase #7 $197.79   13.408%   $224.3097   $224.31   $224.30   $224.30  
  7 purchase totals = $875.20       $956.4450   $956.45   $956.40   $956.40