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 $247.47   10.735%   $274.0359   $274.04   $274.05   $274.00  
  Purchase #2 $57.70   10.484%   $63.7493   $63.75   $63.75   $63.70  
  Purchase #3 $47.25   8.318%   $51.1803   $51.18   $51.20   $51.20  
  Purchase #4 $235.76   7.364%   $253.1214   $253.12   $253.10   $253.10  
  Purchase #5 $117.43   7.217%   $125.9049   $125.90   $125.90   $125.90  
  Purchase #6 $108.48   4.821%   $113.7098   $113.71   $113.70   $113.70  
  Purchase #7 $68.85   10.870%   $76.334   $76.33   $76.35   $76.30  
  7 purchase totals = $882.94       $958.0356   $958.03   $958.05   $957.90