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 $73.69   12.598%   $82.9735   $82.97   $82.95   $83.00  
  Purchase #2 $118.65   11.602%   $132.4158   $132.42   $132.40   $132.40  
  Purchase #3 $166.74   4.370%   $174.0265   $174.03   $174.05   $174.00  
  Purchase #4 $76.89   9.329%   $84.0631   $84.06   $84.05   $84.10  
  Purchase #5 $87.83   3.710%   $91.0885   $91.09   $91.10   $91.10  
  Purchase #6 $92.78   12.215%   $104.1131   $104.11   $104.10   $104.10  
  Purchase #7 $43.98   12.833%   $49.624   $49.62   $49.60   $49.60  
  7 purchase totals = $660.56       $718.3045   $718.30   $718.25   $718.30