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 $44.44   6.103%   $47.1522   $47.15   $47.15   $47.20  
  Purchase #2 $111.87   6.606%   $119.2601   $119.26   $119.25   $119.30  
  Purchase #3 $88.77   6.104%   $94.1885   $94.19   $94.20   $94.20  
  Purchase #4 $27.77   8.336%   $30.0849   $30.08   $30.10   $30.10  
  Purchase #5 $240.51   3.706%   $249.4233   $249.42   $249.40   $249.40  
  Purchase #6 $121.27   12.834%   $136.8338   $136.83   $136.85   $136.80  
  Purchase #7 $185.74   4.676%   $194.4252   $194.43   $194.45   $194.40  
  7 purchase totals = $820.37       $871.3680   $871.36   $871.40   $871.40