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 $110.50   8.357%   $119.7345   $119.73   $119.75   $119.70  
  Purchase #2 $87.26   9.676%   $95.7033   $95.70   $95.70   $95.70  
  Purchase #3 $59.95   10.611%   $66.3113   $66.31   $66.30   $66.30  
  Purchase #4 $188.25   3.759%   $195.3263   $195.33   $195.35   $195.30  
  Purchase #5 $233.90   9.518%   $256.1626   $256.16   $256.15   $256.20  
  Purchase #6 $231.38   5.845%   $244.9042   $244.90   $244.90   $244.90  
  Purchase #7 $14.57   11.592%   $16.259   $16.26   $16.25   $16.30  
  7 purchase totals = $925.81       $994.4012   $994.39   $994.40   $994.40