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 $224.36   13.806%   $255.3351   $255.34   $255.35   $255.30  
  Purchase #2 $195.39   6.737%   $208.5534   $208.55   $208.55   $208.60  
  Purchase #3 $119.92   3.867%   $124.5573   $124.56   $124.55   $124.60  
  Purchase #4 $25.42   3.205%   $26.2347   $26.23   $26.25   $26.20  
  Purchase #5 $240.81   10.301%   $265.6158   $265.62   $265.60   $265.60  
  Purchase #6 $147.44   12.266%   $165.525   $165.53   $165.55   $165.50  
  Purchase #7 $113.36   4.560%   $118.5292   $118.53   $118.55   $118.50  
  7 purchase totals = $1,066.70       $1,164.3505   $1,164.36   $1,164.40   $1,164.30