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 $242.43   4.581%   $253.5357   $253.54   $253.55   $253.50  
  Purchase #2 $89.38   7.330%   $95.9316   $95.93   $95.95   $95.90  
  Purchase #3 $159.81   8.867%   $173.9804   $173.98   $174.00   $174.00  
  Purchase #4 $62.65   9.660%   $68.702   $68.70   $68.70   $68.70  
  Purchase #5 $90.99   8.726%   $98.9298   $98.93   $98.95   $98.90  
  Purchase #6 $138.72   8.480%   $150.4835   $150.48   $150.50   $150.50  
  Purchase #7 $61.35   5.387%   $64.6549   $64.65   $64.65   $64.70  
  7 purchase totals = $845.33       $906.2179   $906.21   $906.30   $906.20