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 $63.59   3.210%   $65.6312   $65.63   $65.65   $65.60  
  Purchase #2 $66.93   8.174%   $72.4009   $72.40   $72.40   $72.40  
  Purchase #3 $60.50   4.668%   $63.3241   $63.32   $63.30   $63.30  
  Purchase #4 $146.28   4.603%   $153.0133   $153.01   $153.00   $153.00  
  Purchase #5 $201.29   13.582%   $228.6292   $228.63   $228.65   $228.60  
  Purchase #6 $196.78   10.549%   $217.5383   $217.54   $217.55   $217.50  
  Purchase #7 $149.83   6.303%   $159.2738   $159.27   $159.25   $159.30  
  7 purchase totals = $885.20       $959.8108   $959.80   $959.80   $959.70