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 $87.95   7.760%   $94.7749   $94.77   $94.75   $94.80  
  Purchase #2 $53.76   10.873%   $59.6053   $59.61   $59.60   $59.60  
  Purchase #3 $90.72   10.488%   $100.2347   $100.23   $100.25   $100.20  
  Purchase #4 $189.89   5.363%   $200.0738   $200.07   $200.05   $200.10  
  Purchase #5 $136.89   8.703%   $148.8035   $148.80   $148.80   $148.80  
  Purchase #6 $21.89   6.239%   $23.2557   $23.26   $23.25   $23.30  
  Purchase #7 $169.42   6.666%   $180.7135   $180.71   $180.70   $180.70  
  7 purchase totals = $750.52       $807.4614   $807.45   $807.40   $807.50