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 $24.38   9.707%   $26.7466   $26.75   $26.75   $26.70  
  Purchase #2 $14.70   7.339%   $15.7788   $15.78   $15.80   $15.80  
  Purchase #3 $174.93   10.389%   $193.1035   $193.10   $193.10   $193.10  
  Purchase #4 $66.76   13.810%   $75.9796   $75.98   $76.00   $76.00  
  Purchase #5 $221.89   6.538%   $236.3972   $236.40   $236.40   $236.40  
  Purchase #6 $198.36   3.492%   $205.2867   $205.29   $205.30   $205.30  
  Purchase #7 $31.48   6.168%   $33.4217   $33.42   $33.40   $33.40  
  7 purchase totals = $732.50       $786.7141   $786.72   $786.75   $786.70