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 $111.99   12.748%   $126.2665   $126.27   $126.25   $126.30  
  Purchase #2 $69.47   10.719%   $76.9165   $76.92   $76.90   $76.90  
  Purchase #3 $49.95   11.555%   $55.7217   $55.72   $55.70   $55.70  
  Purchase #4 $101.52   10.459%   $112.138   $112.14   $112.15   $112.10  
  Purchase #5 $171.57   11.176%   $190.7447   $190.74   $190.75   $190.70  
  Purchase #6 $31.28   3.254%   $32.2979   $32.30   $32.30   $32.30  
  Purchase #7 $52.98   5.608%   $55.9511   $55.95   $55.95   $56.00  
  7 purchase totals = $588.76       $650.0364   $650.04   $650.00   $650.00