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 $86.47   12.401%   $97.1931   $97.19   $97.20   $97.20  
  Purchase #2 $124.77   8.745%   $135.6811   $135.68   $135.70   $135.70  
  Purchase #3 $95.91   8.347%   $103.9156   $103.92   $103.90   $103.90  
  Purchase #4 $147.71   7.711%   $159.0999   $159.10   $159.10   $159.10  
  Purchase #5 $201.90   9.428%   $220.9351   $220.94   $220.95   $220.90  
  Purchase #6 $215.28   8.568%   $233.7252   $233.73   $233.75   $233.70  
  Purchase #7 $229.71   12.302%   $257.9689   $257.97   $257.95   $258.00  
  7 purchase totals = $1,101.75       $1,208.5189   $1,208.53   $1,208.55   $1,208.50