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 $23.52   11.134%   $26.1387   $26.14   $26.15   $26.10  
  Purchase #2 $97.54   3.637%   $101.0875   $101.09   $101.10   $101.10  
  Purchase #3 $69.36   11.449%   $77.301   $77.30   $77.30   $77.30  
  Purchase #4 $118.52   3.382%   $122.5283   $122.53   $122.55   $122.50  
  Purchase #5 $242.79   6.649%   $258.9331   $258.93   $258.95   $258.90  
  Purchase #6 $89.40   11.281%   $99.4852   $99.49   $99.50   $99.50  
  Purchase #7 $201.77   5.754%   $213.3798   $213.38   $213.40   $213.40  
  7 purchase totals = $842.90       $898.8536   $898.86   $898.95   $898.80