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 $60.44   9.431%   $66.1401   $66.14   $66.15   $66.10  
  Purchase #2 $62.86   13.122%   $71.1085   $71.11   $71.10   $71.10  
  Purchase #3 $194.34   9.543%   $212.8859   $212.89   $212.90   $212.90  
  Purchase #4 $29.27   5.855%   $30.9838   $30.98   $31.00   $31.00  
  Purchase #5 $221.54   3.461%   $229.2075   $229.21   $229.20   $229.20  
  Purchase #6 $242.89   10.360%   $268.0534   $268.05   $268.05   $268.10  
  Purchase #7 $67.31   13.739%   $76.5577   $76.56   $76.55   $76.60  
  7 purchase totals = $878.65       $954.9369   $954.94   $954.95   $955.00