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 $117.42   12.563%   $132.1715   $132.17   $132.15   $132.20  
  Purchase #2 $76.82   8.283%   $83.183   $83.18   $83.20   $83.20  
  Purchase #3 $161.92   6.744%   $172.8399   $172.84   $172.85   $172.80  
  Purchase #4 $183.65   7.471%   $197.3705   $197.37   $197.35   $197.40  
  Purchase #5 $55.71   12.522%   $62.686   $62.69   $62.70   $62.70  
  Purchase #6 $93.97   11.216%   $104.5097   $104.51   $104.50   $104.50  
  Purchase #7 $72.48   12.849%   $81.793   $81.79   $81.80   $81.80  
  7 purchase totals = $761.97       $834.5536   $834.55   $834.55   $834.60