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 $119.32   4.725%   $124.9579   $124.96   $124.95   $125.00  
  Purchase #2 $204.59   13.317%   $231.8353   $231.84   $231.85   $231.80  
  Purchase #3 $118.40   7.166%   $126.8845   $126.88   $126.90   $126.90  
  Purchase #4 $73.63   3.518%   $76.2203   $76.22   $76.20   $76.20  
  Purchase #5 $113.91   6.858%   $121.7219   $121.72   $121.70   $121.70  
  Purchase #6 $65.95   13.478%   $74.8387   $74.84   $74.85   $74.80  
  Purchase #7 $190.29   12.296%   $213.6881   $213.69   $213.70   $213.70  
  7 purchase totals = $886.09       $970.1467   $970.15   $970.15   $970.10