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 $245.25   12.406%   $275.6757   $275.68   $275.70   $275.70  
  Purchase #2 $67.25   7.259%   $72.1317   $72.13   $72.15   $72.10  
  Purchase #3 $214.88   6.845%   $229.5885   $229.59   $229.60   $229.60  
  Purchase #4 $242.86   4.566%   $253.949   $253.95   $253.95   $253.90  
  Purchase #5 $86.49   8.225%   $93.6038   $93.60   $93.60   $93.60  
  Purchase #6 $52.27   12.634%   $58.8738   $58.87   $58.85   $58.90  
  Purchase #7 $46.42   3.502%   $48.0456   $48.05   $48.05   $48.00  
  7 purchase totals = $955.42       $1,031.8681   $1,031.87   $1,031.90   $1,031.80