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 $57.97   8.716%   $63.0227   $63.02   $63.00   $63.00  
  Purchase #2 $52.64   3.688%   $54.5814   $54.58   $54.60   $54.60  
  Purchase #3 $155.60   11.177%   $172.9914   $172.99   $173.00   $173.00  
  Purchase #4 $108.47   8.113%   $117.2702   $117.27   $117.25   $117.30  
  Purchase #5 $143.25   12.103%   $160.5875   $160.59   $160.60   $160.60  
  Purchase #6 $73.43   11.237%   $81.6813   $81.68   $81.70   $81.70  
  Purchase #7 $136.91   10.627%   $151.4594   $151.46   $151.45   $151.50  
  7 purchase totals = $728.27       $801.5939   $801.59   $801.60   $801.70