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 $89.56   4.612%   $93.6905   $93.69   $93.70   $93.70  
  Purchase #2 $122.34   11.842%   $136.8275   $136.83   $136.85   $136.80  
  Purchase #3 $235.49   11.342%   $262.1993   $262.20   $262.20   $262.20  
  Purchase #4 $104.92   10.862%   $116.3164   $116.32   $116.30   $116.30  
  Purchase #5 $44.98   3.784%   $46.682   $46.68   $46.70   $46.70  
  Purchase #6 $97.80   11.120%   $108.6754   $108.68   $108.70   $108.70  
  Purchase #7 $88.70   7.383%   $95.2487   $95.25   $95.25   $95.20  
  7 purchase totals = $783.79       $859.6398   $859.65   $859.70   $859.60