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 $26.34   3.674%   $27.3077   $27.31   $27.30   $27.30  
  Purchase #2 $87.96   5.683%   $92.9588   $92.96   $92.95   $93.00  
  Purchase #3 $70.90   7.491%   $76.2111   $76.21   $76.20   $76.20  
  Purchase #4 $69.96   11.390%   $77.9284   $77.93   $77.95   $77.90  
  Purchase #5 $232.28   6.166%   $246.6024   $246.60   $246.60   $246.60  
  Purchase #6 $94.92   8.642%   $103.123   $103.12   $103.10   $103.10  
  Purchase #7 $103.42   9.858%   $113.6151   $113.62   $113.60   $113.60  
  7 purchase totals = $685.78       $737.7465   $737.75   $737.70   $737.70