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 $148.73   4.871%   $155.9746   $155.97   $155.95   $156.00  
  Purchase #2 $150.61   12.615%   $169.6095   $169.61   $169.60   $169.60  
  Purchase #3 $69.46   6.814%   $74.193   $74.19   $74.20   $74.20  
  Purchase #4 $44.46   8.251%   $48.1284   $48.13   $48.15   $48.10  
  Purchase #5 $152.94   4.811%   $160.2979   $160.30   $160.30   $160.30  
  Purchase #6 $209.80   12.591%   $236.2159   $236.22   $236.20   $236.20  
  Purchase #7 $163.69   4.215%   $170.5895   $170.59   $170.60   $170.60  
  7 purchase totals = $939.69       $1,015.0088   $1,015.01   $1,015.00   $1,015.00