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 $61.99   8.533%   $67.2796   $67.28   $67.30   $67.30  
  Purchase #2 $52.42   9.278%   $57.2835   $57.28   $57.30   $57.30  
  Purchase #3 $132.38   3.454%   $136.9524   $136.95   $136.95   $137.00  
  Purchase #4 $86.31   13.164%   $97.6718   $97.67   $97.65   $97.70  
  Purchase #5 $54.33   12.616%   $61.1843   $61.18   $61.20   $61.20  
  Purchase #6 $90.78   3.411%   $93.8765   $93.88   $93.90   $93.90  
  Purchase #7 $15.90   6.586%   $16.9472   $16.95   $16.95   $16.90  
  7 purchase totals = $494.11       $531.1953   $531.19   $531.25   $531.30