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 $95.64   3.421%   $98.9118   $98.91   $98.90   $98.90  
  Purchase #2 $104.92   4.775%   $109.9299   $109.93   $109.95   $109.90  
  Purchase #3 $159.47   5.658%   $168.4928   $168.49   $168.50   $168.50  
  Purchase #4 $244.76   7.747%   $263.7216   $263.72   $263.70   $263.70  
  Purchase #5 $148.79   4.594%   $155.6254   $155.63   $155.65   $155.60  
  Purchase #6 $97.52   4.840%   $102.24   $102.24   $102.25   $102.20  
  Purchase #7 $84.73   9.597%   $92.8615   $92.86   $92.85   $92.90  
  7 purchase totals = $935.83       $991.7830   $991.78   $991.80   $991.70