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 $41.99   13.663%   $47.7271   $47.73   $47.75   $47.70  
  Purchase #2 $221.61   3.450%   $229.2555   $229.26   $229.25   $229.30  
  Purchase #3 $98.91   9.236%   $108.0453   $108.05   $108.05   $108.00  
  Purchase #4 $117.26   7.581%   $126.1495   $126.15   $126.15   $126.10  
  Purchase #5 $166.50   4.807%   $174.5037   $174.50   $174.50   $174.50  
  Purchase #6 $72.75   5.470%   $76.7294   $76.73   $76.75   $76.70  
  Purchase #7 $84.66   9.701%   $92.8729   $92.87   $92.85   $92.90  
  7 purchase totals = $803.68       $855.2834   $855.29   $855.30   $855.20