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 $66.39   10.283%   $73.2169   $73.22   $73.20   $73.20  
  Purchase #2 $11.60   4.483%   $12.12   $12.12   $12.10   $12.10  
  Purchase #3 $127.27   9.595%   $139.4816   $139.48   $139.50   $139.50  
  Purchase #4 $46.76   3.808%   $48.5406   $48.54   $48.55   $48.50  
  Purchase #5 $60.86   10.613%   $67.3191   $67.32   $67.30   $67.30  
  Purchase #6 $60.27   13.508%   $68.4113   $68.41   $68.40   $68.40  
  Purchase #7 $61.87   8.142%   $66.9075   $66.91   $66.90   $66.90  
  7 purchase totals = $435.02       $475.9970   $476.00   $475.95   $475.90