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 $87.38   5.795%   $92.4437   $92.44   $92.45   $92.40  
  Purchase #2 $24.50   3.130%   $25.2669   $25.27   $25.25   $25.30  
  Purchase #3 $85.74   13.715%   $97.4992   $97.50   $97.50   $97.50  
  Purchase #4 $230.80   9.294%   $252.2506   $252.25   $252.25   $252.30  
  Purchase #5 $163.99   13.282%   $185.7712   $185.77   $185.75   $185.80  
  Purchase #6 $151.27   6.639%   $161.3128   $161.31   $161.30   $161.30  
  Purchase #7 $15.66   6.839%   $16.731   $16.73   $16.75   $16.70  
  7 purchase totals = $759.34       $831.2754   $831.27   $831.25   $831.30