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 $114.32   3.239%   $118.0228   $118.02   $118.00   $118.00  
  Purchase #2 $202.33   12.674%   $227.9733   $227.97   $227.95   $228.00  
  Purchase #3 $117.69   6.834%   $125.7329   $125.73   $125.75   $125.70  
  Purchase #4 $246.83   4.278%   $257.3894   $257.39   $257.40   $257.40  
  Purchase #5 $43.87   8.391%   $47.5511   $47.55   $47.55   $47.60  
  Purchase #6 $116.26   8.855%   $126.5548   $126.55   $126.55   $126.60  
  Purchase #7 $242.72   12.549%   $273.1789   $273.18   $273.20   $273.20  
  7 purchase totals = $1,084.02       $1,176.4032   $1,176.39   $1,176.40   $1,176.50