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 $95.73   4.353%   $99.8971   $99.90   $99.90   $99.90  
  Purchase #2 $8.95   3.595%   $9.2718   $9.27   $9.25   $9.30  
  Purchase #3 $53.45   8.466%   $57.9751   $57.98   $58.00   $58.00  
  Purchase #4 $241.69   4.114%   $251.6331   $251.63   $251.65   $251.60  
  Purchase #5 $27.54   6.538%   $29.3406   $29.34   $29.35   $29.30  
  Purchase #6 $110.98   5.167%   $116.7143   $116.71   $116.70   $116.70  
  Purchase #7 $117.61   6.468%   $125.217   $125.22   $125.20   $125.20  
  7 purchase totals = $655.95       $690.0490   $690.05   $690.05   $690.00