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 $182.32   6.831%   $194.7743   $194.77   $194.75   $194.80  
  Purchase #2 $32.54   10.841%   $36.0677   $36.07   $36.05   $36.10  
  Purchase #3 $231.77   13.515%   $263.0937   $263.09   $263.10   $263.10  
  Purchase #4 $41.46   3.697%   $42.9928   $42.99   $43.00   $43.00  
  Purchase #5 $165.26   7.859%   $178.2478   $178.25   $178.25   $178.20  
  Purchase #6 $136.69   7.326%   $146.7039   $146.70   $146.70   $146.70  
  Purchase #7 $86.37   9.269%   $94.3756   $94.38   $94.40   $94.40  
  7 purchase totals = $876.41       $956.2558   $956.25   $956.25   $956.30