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 $22.86   4.779%   $23.9525   $23.95   $23.95   $24.00  
  Purchase #2 $93.65   8.437%   $101.5513   $101.55   $101.55   $101.60  
  Purchase #3 $82.65   9.392%   $90.4125   $90.41   $90.40   $90.40  
  Purchase #4 $154.69   9.342%   $169.1411   $169.14   $169.15   $169.10  
  Purchase #5 $247.55   4.136%   $257.7887   $257.79   $257.80   $257.80  
  Purchase #6 $173.66   6.592%   $185.1077   $185.11   $185.10   $185.10  
  Purchase #7 $138.42   11.645%   $154.539   $154.54   $154.55   $154.50  
  7 purchase totals = $913.48       $982.4928   $982.49   $982.50   $982.50