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 $64.25   6.731%   $68.5747   $68.57   $68.55   $68.60  
  Purchase #2 $129.65   8.313%   $140.4278   $140.43   $140.45   $140.40  
  Purchase #3 $233.53   12.289%   $262.2285   $262.23   $262.25   $262.20  
  Purchase #4 $53.30   8.236%   $57.6898   $57.69   $57.70   $57.70  
  Purchase #5 $104.85   13.306%   $118.8013   $118.80   $118.80   $118.80  
  Purchase #6 $30.91   10.667%   $34.2072   $34.21   $34.20   $34.20  
  Purchase #7 $218.38   8.417%   $236.761   $236.76   $236.75   $236.80  
  7 purchase totals = $834.87       $918.6903   $918.69   $918.70   $918.70