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 $64.78   3.732%   $67.1976   $67.20   $67.20   $67.20  
  Purchase #2 $104.28   11.818%   $116.6038   $116.60   $116.60   $116.60  
  Purchase #3 $144.68   12.749%   $163.1253   $163.13   $163.15   $163.10  
  Purchase #4 $80.69   6.130%   $85.6363   $85.64   $85.65   $85.60  
  Purchase #5 $175.62   6.564%   $187.1477   $187.15   $187.15   $187.10  
  Purchase #6 $200.30   4.675%   $209.664   $209.66   $209.65   $209.70  
  Purchase #7 $112.26   6.192%   $119.2111   $119.21   $119.20   $119.20  
  7 purchase totals = $882.61       $948.5858   $948.59   $948.60   $948.50