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 $22.86   3.239%   $23.6004   $23.60   $23.60   $23.60  
  Purchase #2 $115.52   9.392%   $126.3696   $126.37   $126.35   $126.40  
  Purchase #3 $55.80   8.661%   $60.6328   $60.63   $60.65   $60.60  
  Purchase #4 $151.92   8.434%   $164.7329   $164.73   $164.75   $164.70  
  Purchase #5 $149.55   10.412%   $165.1211   $165.12   $165.10   $165.10  
  Purchase #6 $128.42   11.619%   $143.3411   $143.34   $143.35   $143.30  
  Purchase #7 $61.57   12.827%   $69.4676   $69.47   $69.45   $69.50  
  7 purchase totals = $685.64       $753.2655   $753.26   $753.25   $753.20