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   8.135%   $93.7314   $93.73   $93.75   $93.70  
  Purchase #2 $42.82   5.186%   $45.0406   $45.04   $45.05   $45.00  
  Purchase #3 $182.46   6.594%   $194.4914   $194.49   $194.50   $194.50  
  Purchase #4 $53.62   12.798%   $60.4823   $60.48   $60.50   $60.50  
  Purchase #5 $89.66   10.648%   $99.207   $99.21   $99.20   $99.20  
  Purchase #6 $148.69   12.484%   $167.2525   $167.25   $167.25   $167.30  
  Purchase #7 $92.86   5.874%   $98.3146   $98.31   $98.30   $98.30  
  7 purchase totals = $696.79       $758.5198   $758.51   $758.55   $758.50