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 $246.42   8.598%   $267.6072   $267.61   $267.60   $267.60  
  Purchase #2 $163.53   11.391%   $182.1577   $182.16   $182.15   $182.20  
  Purchase #3 $110.70   6.226%   $117.5922   $117.59   $117.60   $117.60  
  Purchase #4 $86.32   5.269%   $90.8682   $90.87   $90.85   $90.90  
  Purchase #5 $72.40   12.337%   $81.332   $81.33   $81.35   $81.30  
  Purchase #6 $51.87   12.251%   $58.2246   $58.22   $58.20   $58.20  
  Purchase #7 $22.93   6.729%   $24.473   $24.47   $24.45   $24.50  
  7 purchase totals = $754.17       $822.2549   $822.25   $822.20   $822.30