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 $157.65   3.360%   $162.947   $162.95   $162.95   $162.90  
  Purchase #2 $60.96   8.832%   $66.344   $66.34   $66.35   $66.30  
  Purchase #3 $239.75   7.113%   $256.8034   $256.80   $256.80   $256.80  
  Purchase #4 $82.98   7.605%   $89.2906   $89.29   $89.30   $89.30  
  Purchase #5 $31.50   11.186%   $35.0236   $35.02   $35.00   $35.00  
  Purchase #6 $237.54   5.116%   $249.6925   $249.69   $249.70   $249.70  
  Purchase #7 $59.68   8.436%   $64.7146   $64.71   $64.70   $64.70  
  7 purchase totals = $870.06       $924.8157   $924.80   $924.80   $924.70