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 $79.55   5.242%   $83.72   $83.72   $83.70   $83.70  
  Purchase #2 $13.67   3.347%   $14.1275   $14.13   $14.15   $14.10  
  Purchase #3 $248.69   8.358%   $269.4755   $269.48   $269.50   $269.50  
  Purchase #4 $151.78   10.277%   $167.3784   $167.38   $167.40   $167.40  
  Purchase #5 $124.75   6.267%   $132.5681   $132.57   $132.55   $132.60  
  Purchase #6 $133.29   9.736%   $146.2671   $146.27   $146.25   $146.30  
  Purchase #7 $100.73   12.719%   $113.5418   $113.54   $113.55   $113.50  
  7 purchase totals = $852.46       $927.0784   $927.09   $927.10   $927.10