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 $61.48   4.749%   $64.3997   $64.40   $64.40   $64.40  
  Purchase #2 $239.81   7.690%   $258.2514   $258.25   $258.25   $258.30  
  Purchase #3 $83.78   11.679%   $93.5647   $93.56   $93.55   $93.60  
  Purchase #4 $209.45   7.657%   $225.4876   $225.49   $225.50   $225.50  
  Purchase #5 $18.28   11.575%   $20.3959   $20.40   $20.40   $20.40  
  Purchase #6 $171.96   11.356%   $191.4878   $191.49   $191.50   $191.50  
  Purchase #7 $236.98   3.185%   $244.5278   $244.53   $244.55   $244.50  
  7 purchase totals = $1,021.74       $1,098.1149   $1,098.12   $1,098.15   $1,098.20