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 $54.97   11.620%   $61.3575   $61.36   $61.35   $61.40  
  Purchase #2 $121.85   8.793%   $132.5643   $132.56   $132.55   $132.60  
  Purchase #3 $195.53   6.369%   $207.9833   $207.98   $208.00   $208.00  
  Purchase #4 $174.57   10.860%   $193.5283   $193.53   $193.55   $193.50  
  Purchase #5 $9.81   9.326%   $10.7249   $10.72   $10.70   $10.70  
  Purchase #6 $57.26   8.609%   $62.1895   $62.19   $62.20   $62.20  
  Purchase #7 $217.48   11.347%   $242.1575   $242.16   $242.15   $242.20  
  7 purchase totals = $831.47       $910.5053   $910.50   $910.50   $910.60