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 $57.76   10.859%   $64.0322   $64.03   $64.05   $64.00  
  Purchase #2 $250.71   3.708%   $260.0063   $260.01   $260.00   $260.00  
  Purchase #3 $119.93   11.164%   $133.319   $133.32   $133.30   $133.30  
  Purchase #4 $28.80   5.729%   $30.45   $30.45   $30.45   $30.50  
  Purchase #5 $228.57   8.388%   $247.7425   $247.74   $247.75   $247.70  
  Purchase #6 $204.39   3.669%   $211.8891   $211.89   $211.90   $211.90  
  Purchase #7 $160.67   4.820%   $168.4143   $168.41   $168.40   $168.40  
  7 purchase totals = $1,050.83       $1,115.8534   $1,115.85   $1,115.85   $1,115.80