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 $66.41   9.639%   $72.8113   $72.81   $72.80   $72.80  
  Purchase #2 $158.77   12.353%   $178.3829   $178.38   $178.40   $178.40  
  Purchase #3 $200.82   9.406%   $219.7091   $219.71   $219.70   $219.70  
  Purchase #4 $49.28   11.713%   $55.0522   $55.05   $55.05   $55.10  
  Purchase #5 $61.55   6.746%   $65.7022   $65.70   $65.70   $65.70  
  Purchase #6 $72.25   4.634%   $75.5981   $75.60   $75.60   $75.60  
  Purchase #7 $177.58   10.219%   $195.7269   $195.73   $195.75   $195.70  
  7 purchase totals = $786.66       $862.9827   $862.98   $863.00   $863.00