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 $154.58   10.460%   $170.7491   $170.75   $170.75   $170.70  
  Purchase #2 $115.59   5.445%   $121.8839   $121.88   $121.90   $121.90  
  Purchase #3 $239.81   9.464%   $262.5056   $262.51   $262.50   $262.50  
  Purchase #4 $224.40   5.158%   $235.9746   $235.97   $235.95   $236.00  
  Purchase #5 $227.38   11.762%   $254.1244   $254.12   $254.10   $254.10  
  Purchase #6 $191.64   8.234%   $207.4196   $207.42   $207.40   $207.40  
  Purchase #7 $149.87   5.649%   $158.3362   $158.34   $158.35   $158.30  
  7 purchase totals = $1,303.27       $1,410.9934   $1,410.99   $1,410.95   $1,410.90