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 $104.26   12.227%   $117.0079   $117.01   $117.00   $117.00  
  Purchase #2 $245.62   8.771%   $267.1633   $267.16   $267.15   $267.20  
  Purchase #3 $210.54   8.835%   $229.1412   $229.14   $229.15   $229.10  
  Purchase #4 $30.97   9.206%   $33.8211   $33.82   $33.80   $33.80  
  Purchase #5 $188.51   13.771%   $214.4697   $214.47   $214.45   $214.50  
  Purchase #6 $246.57   6.159%   $261.7562   $261.76   $261.75   $261.80  
  Purchase #7 $113.46   13.854%   $129.1787   $129.18   $129.20   $129.20  
  7 purchase totals = $1,139.93       $1,252.5381   $1,252.54   $1,252.50   $1,252.60