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 $236.82   3.388%   $244.8435   $244.84   $244.85   $244.80  
  Purchase #2 $96.99   4.276%   $101.1373   $101.14   $101.15   $101.10  
  Purchase #3 $71.49   6.550%   $76.1726   $76.17   $76.15   $76.20  
  Purchase #4 $127.84   7.202%   $137.047   $137.05   $137.05   $137.00  
  Purchase #5 $121.60   3.763%   $126.1758   $126.18   $126.20   $126.20  
  Purchase #6 $51.96   11.816%   $58.0996   $58.10   $58.10   $58.10  
  Purchase #7 $53.81   5.198%   $56.607   $56.61   $56.60   $56.60  
  7 purchase totals = $760.51       $800.0828   $800.09   $800.10   $800.00