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 $86.48   12.543%   $97.3272   $97.33   $97.35   $97.30  
  Purchase #2 $121.33   4.544%   $126.8432   $126.84   $126.85   $126.80  
  Purchase #3 $72.27   13.104%   $81.7403   $81.74   $81.75   $81.70  
  Purchase #4 $62.45   13.208%   $70.6984   $70.70   $70.70   $70.70  
  Purchase #5 $229.88   13.639%   $261.2333   $261.23   $261.25   $261.20  
  Purchase #6 $52.80   11.223%   $58.7257   $58.73   $58.75   $58.70  
  Purchase #7 $22.65   4.178%   $23.5963   $23.60   $23.60   $23.60  
  7 purchase totals = $647.86       $720.1644   $720.17   $720.25   $720.00