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 $90.83   5.171%   $95.5268   $95.53   $95.55   $95.50  
  Purchase #2 $108.63   7.109%   $116.3525   $116.35   $116.35   $116.40  
  Purchase #3 $7.93   11.123%   $8.8121   $8.81   $8.80   $8.80  
  Purchase #4 $13.49   5.492%   $14.2309   $14.23   $14.25   $14.20  
  Purchase #5 $45.64   11.502%   $50.8895   $50.89   $50.90   $50.90  
  Purchase #6 $199.99   5.330%   $210.6495   $210.65   $210.65   $210.60  
  Purchase #7 $103.36   8.380%   $112.0216   $112.02   $112.00   $112.00  
  7 purchase totals = $569.87       $608.4829   $608.48   $608.50   $608.40