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 $64.63   5.461%   $68.1594   $68.16   $68.15   $68.20  
  Purchase #2 $90.99   3.384%   $94.0691   $94.07   $94.05   $94.10  
  Purchase #3 $70.98   6.733%   $75.7591   $75.76   $75.75   $75.80  
  Purchase #4 $213.37   5.213%   $224.493   $224.49   $224.50   $224.50  
  Purchase #5 $152.82   6.499%   $162.7518   $162.75   $162.75   $162.80  
  Purchase #6 $53.40   4.384%   $55.7411   $55.74   $55.75   $55.70  
  Purchase #7 $201.43   4.284%   $210.0593   $210.06   $210.05   $210.10  
  7 purchase totals = $847.62       $891.0328   $891.03   $891.00   $891.20