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 $62.98   6.719%   $67.2116   $67.21   $67.20   $67.20  
  Purchase #2 $227.28   10.842%   $251.9217   $251.92   $251.90   $251.90  
  Purchase #3 $8.59   12.772%   $9.6871   $9.69   $9.70   $9.70  
  Purchase #4 $146.98   9.874%   $161.4928   $161.49   $161.50   $161.50  
  Purchase #5 $50.58   4.229%   $52.719   $52.72   $52.70   $52.70  
  Purchase #6 $236.35   5.639%   $249.6778   $249.68   $249.70   $249.70  
  Purchase #7 $45.36   7.183%   $48.6182   $48.62   $48.60   $48.60  
  7 purchase totals = $778.12       $841.3282   $841.33   $841.30   $841.30