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 $152.37   12.613%   $171.5884   $171.59   $171.60   $171.60  
  Purchase #2 $66.51   6.293%   $70.6955   $70.70   $70.70   $70.70  
  Purchase #3 $125.89   8.470%   $136.5529   $136.55   $136.55   $136.60  
  Purchase #4 $97.45   10.462%   $107.6452   $107.65   $107.65   $107.60  
  Purchase #5 $230.74   10.200%   $254.2755   $254.28   $254.30   $254.30  
  Purchase #6 $121.34   4.290%   $126.5455   $126.55   $126.55   $126.50  
  Purchase #7 $89.90   12.548%   $101.1807   $101.18   $101.20   $101.20  
  7 purchase totals = $884.20       $968.4837   $968.50   $968.55   $968.50