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 $233.79   7.108%   $250.4078   $250.41   $250.40   $250.40  
  Purchase #2 $226.98   12.459%   $255.2594   $255.26   $255.25   $255.30  
  Purchase #3 $199.56   6.715%   $212.9605   $212.96   $212.95   $213.00  
  Purchase #4 $19.43   4.371%   $20.2793   $20.28   $20.30   $20.30  
  Purchase #5 $77.88   10.175%   $85.8043   $85.80   $85.80   $85.80  
  Purchase #6 $36.92   8.478%   $40.0501   $40.05   $40.05   $40.10  
  Purchase #7 $76.44   10.642%   $84.5747   $84.57   $84.55   $84.60  
  7 purchase totals = $871.00       $949.3361   $949.33   $949.30   $949.50