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 $55.57   11.515%   $61.9689   $61.97   $61.95   $62.00  
  Purchase #2 $111.44   4.395%   $116.3378   $116.34   $116.35   $116.30  
  Purchase #3 $137.45   9.271%   $150.193   $150.19   $150.20   $150.20  
  Purchase #4 $214.45   5.687%   $226.6458   $226.65   $226.65   $226.60  
  Purchase #5 $55.37   8.324%   $59.979   $59.98   $60.00   $60.00  
  Purchase #6 $102.43   9.162%   $111.8146   $111.81   $111.80   $111.80  
  Purchase #7 $191.50   13.812%   $217.95   $217.95   $217.95   $218.00  
  7 purchase totals = $868.21       $944.8891   $944.89   $944.90   $944.90