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 $17.88   4.198%   $18.6306   $18.63   $18.65   $18.60  
  Purchase #2 $160.45   11.350%   $178.6611   $178.66   $178.65   $178.70  
  Purchase #3 $137.25   3.559%   $142.1347   $142.13   $142.15   $142.10  
  Purchase #4 $146.62   11.131%   $162.9403   $162.94   $162.95   $162.90  
  Purchase #5 $36.48   13.814%   $41.5193   $41.52   $41.50   $41.50  
  Purchase #6 $56.89   7.381%   $61.0891   $61.09   $61.10   $61.10  
  Purchase #7 $194.82   9.178%   $212.7006   $212.70   $212.70   $212.70  
  7 purchase totals = $750.39       $817.6757   $817.67   $817.70   $817.60