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 $66.69   10.443%   $73.6544   $73.65   $73.65   $73.70  
  Purchase #2 $23.64   11.831%   $26.4368   $26.44   $26.45   $26.40  
  Purchase #3 $54.62   12.142%   $61.252   $61.25   $61.25   $61.30  
  Purchase #4 $224.64   4.549%   $234.8589   $234.86   $234.85   $234.90  
  Purchase #5 $85.53   12.186%   $95.9527   $95.95   $95.95   $96.00  
  Purchase #6 $68.83   12.312%   $77.3043   $77.30   $77.30   $77.30  
  Purchase #7 $12.63   6.459%   $13.4458   $13.45   $13.45   $13.40  
  7 purchase totals = $536.58       $582.9049   $582.90   $582.90   $583.00