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 $107.46   13.847%   $122.34   $122.34   $122.35   $122.30  
  Purchase #2 $144.31   7.134%   $154.6051   $154.61   $154.60   $154.60  
  Purchase #3 $78.42   7.844%   $84.5713   $84.57   $84.55   $84.60  
  Purchase #4 $170.96   11.652%   $190.8803   $190.88   $190.90   $190.90  
  Purchase #5 $125.86   13.335%   $142.6434   $142.64   $142.65   $142.60  
  Purchase #6 $41.40   8.541%   $44.936   $44.94   $44.95   $44.90  
  Purchase #7 $45.99   13.677%   $52.2801   $52.28   $52.30   $52.30  
  7 purchase totals = $714.40       $792.2562   $792.26   $792.30   $792.20