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 $74.71   13.696%   $84.9423   $84.94   $84.95   $84.90  
  Purchase #2 $149.54   10.711%   $165.5572   $165.56   $165.55   $165.60  
  Purchase #3 $60.65   13.154%   $68.6279   $68.63   $68.65   $68.60  
  Purchase #4 $213.62   13.186%   $241.7879   $241.79   $241.80   $241.80  
  Purchase #5 $98.53   6.701%   $105.1325   $105.13   $105.15   $105.10  
  Purchase #6 $7.40   5.487%   $7.806   $7.81   $7.80   $7.80  
  Purchase #7 $72.67   12.788%   $81.963   $81.96   $81.95   $82.00  
  7 purchase totals = $677.12       $755.8168   $755.82   $755.85   $755.80