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 $56.54   7.489%   $60.7743   $60.77   $60.75   $60.80  
  Purchase #2 $217.40   12.649%   $244.8989   $244.90   $244.90   $244.90  
  Purchase #3 $207.41   13.807%   $236.0471   $236.05   $236.05   $236.00  
  Purchase #4 $204.83   10.507%   $226.3515   $226.35   $226.35   $226.40  
  Purchase #5 $5.85   13.811%   $6.6579   $6.66   $6.65   $6.70  
  Purchase #6 $56.81   9.383%   $62.1405   $62.14   $62.15   $62.10  
  Purchase #7 $215.83   5.130%   $226.9021   $226.90   $226.90   $226.90  
  7 purchase totals = $964.67       $1,063.7723   $1,063.77   $1,063.75   $1,063.80