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 $38.43   10.694%   $42.5397   $42.54   $42.55   $42.50  
  Purchase #2 $65.64   5.124%   $69.0034   $69.00   $69.00   $69.00  
  Purchase #3 $62.48   11.438%   $69.6265   $69.63   $69.65   $69.60  
  Purchase #4 $209.30   8.388%   $226.8561   $226.86   $226.85   $226.90  
  Purchase #5 $153.96   10.735%   $170.4876   $170.49   $170.50   $170.50  
  Purchase #6 $195.38   9.504%   $213.9489   $213.95   $213.95   $213.90  
  Purchase #7 $175.97   4.705%   $184.2494   $184.25   $184.25   $184.20  
  7 purchase totals = $901.16       $976.7116   $976.72   $976.75   $976.60