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 $54.63   8.803%   $59.4391   $59.44   $59.45   $59.40  
  Purchase #2 $195.35   3.591%   $202.365   $202.37   $202.35   $202.40  
  Purchase #3 $239.58   4.249%   $249.7598   $249.76   $249.75   $249.80  
  Purchase #4 $234.83   10.655%   $259.8511   $259.85   $259.85   $259.90  
  Purchase #5 $27.75   4.431%   $28.9796   $28.98   $29.00   $29.00  
  Purchase #6 $38.29   10.866%   $42.4506   $42.45   $42.45   $42.50  
  Purchase #7 $144.55   6.797%   $154.3751   $154.38   $154.40   $154.40  
  7 purchase totals = $934.98       $997.2203   $997.23   $997.25   $997.40