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 $212.44   13.521%   $241.164   $241.16   $241.15   $241.20  
  Purchase #2 $216.58   13.267%   $245.3137   $245.31   $245.30   $245.30  
  Purchase #3 $226.64   13.631%   $257.5333   $257.53   $257.55   $257.50  
  Purchase #4 $81.82   3.233%   $84.4652   $84.47   $84.45   $84.50  
  Purchase #5 $86.33   9.738%   $94.7368   $94.74   $94.75   $94.70  
  Purchase #6 $231.90   11.515%   $258.6033   $258.60   $258.60   $258.60  
  Purchase #7 $165.70   10.116%   $182.4622   $182.46   $182.45   $182.50  
  7 purchase totals = $1,221.41       $1,364.2785   $1,364.27   $1,364.25   $1,364.30