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 $50.69   12.162%   $56.8549   $56.85   $56.85   $56.90  
  Purchase #2 $25.46   5.670%   $26.9036   $26.90   $26.90   $26.90  
  Purchase #3 $66.45   12.856%   $74.9928   $74.99   $75.00   $75.00  
  Purchase #4 $148.35   3.328%   $153.2871   $153.29   $153.30   $153.30  
  Purchase #5 $250.38   3.647%   $259.5114   $259.51   $259.50   $259.50  
  Purchase #6 $144.36   12.694%   $162.6851   $162.69   $162.70   $162.70  
  Purchase #7 $61.45   9.664%   $67.3885   $67.39   $67.40   $67.40  
  7 purchase totals = $747.14       $801.6234   $801.62   $801.65   $801.70