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 $42.41   5.140%   $44.5899   $44.59   $44.60   $44.60  
  Purchase #2 $239.32   8.788%   $260.3514   $260.35   $260.35   $260.40  
  Purchase #3 $94.51   3.143%   $97.4804   $97.48   $97.50   $97.50  
  Purchase #4 $230.74   10.571%   $255.1315   $255.13   $255.15   $255.10  
  Purchase #5 $64.58   13.163%   $73.0807   $73.08   $73.10   $73.10  
  Purchase #6 $102.98   5.486%   $108.6295   $108.63   $108.65   $108.60  
  Purchase #7 $214.76   3.572%   $222.4312   $222.43   $222.45   $222.40  
  7 purchase totals = $989.30       $1,061.6946   $1,061.69   $1,061.80   $1,061.70