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 $91.38   7.228%   $97.9849   $97.98   $98.00   $98.00  
  Purchase #2 $236.96   8.780%   $257.7651   $257.77   $257.75   $257.80  
  Purchase #3 $164.96   10.810%   $182.7922   $182.79   $182.80   $182.80  
  Purchase #4 $183.87   10.226%   $202.6725   $202.67   $202.65   $202.70  
  Purchase #5 $215.62   11.786%   $241.033   $241.03   $241.05   $241.00  
  Purchase #6 $54.88   4.778%   $57.5022   $57.50   $57.50   $57.50  
  Purchase #7 $113.99   10.764%   $126.2599   $126.26   $126.25   $126.30  
  7 purchase totals = $1,061.66       $1,166.0098   $1,166.00   $1,166.00   $1,166.10