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 $44.99   8.132%   $48.6486   $48.65   $48.65   $48.60  
  Purchase #2 $213.38   9.833%   $234.3617   $234.36   $234.35   $234.40  
  Purchase #3 $95.49   9.435%   $104.4995   $104.50   $104.50   $104.50  
  Purchase #4 $62.73   12.505%   $70.5744   $70.57   $70.55   $70.60  
  Purchase #5 $112.32   8.106%   $121.4247   $121.42   $121.40   $121.40  
  Purchase #6 $186.55   5.594%   $196.9856   $196.99   $197.00   $197.00  
  Purchase #7 $243.33   7.473%   $261.5141   $261.51   $261.50   $261.50  
  7 purchase totals = $958.79       $1,038.0086   $1,038.00   $1,037.95   $1,038.00