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 $86.68   12.199%   $97.2541   $97.25   $97.25   $97.30  
  Purchase #2 $170.60   7.754%   $183.8283   $183.83   $183.85   $183.80  
  Purchase #3 $24.30   12.528%   $27.3443   $27.34   $27.35   $27.30  
  Purchase #4 $92.67   6.856%   $99.0235   $99.02   $99.00   $99.00  
  Purchase #5 $61.68   4.611%   $64.5241   $64.52   $64.50   $64.50  
  Purchase #6 $153.35   4.522%   $160.2845   $160.28   $160.30   $160.30  
  Purchase #7 $228.77   4.797%   $239.7441   $239.74   $239.75   $239.70  
  7 purchase totals = $818.05       $872.0029   $871.98   $872.00   $871.90