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 $156.84   12.866%   $177.019   $177.02   $177.00   $177.00  
  Purchase #2 $212.81   5.389%   $224.2783   $224.28   $224.30   $224.30  
  Purchase #3 $245.26   13.259%   $277.779   $277.78   $277.80   $277.80  
  Purchase #4 $237.60   5.114%   $249.7509   $249.75   $249.75   $249.80  
  Purchase #5 $57.71   13.129%   $65.2867   $65.29   $65.30   $65.30  
  Purchase #6 $108.38   11.596%   $120.9477   $120.95   $120.95   $120.90  
  Purchase #7 $201.92   7.860%   $217.7909   $217.79   $217.80   $217.80  
  7 purchase totals = $1,220.52       $1,332.8525   $1,332.86   $1,332.90   $1,332.90