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 $65.26   12.776%   $73.5976   $73.60   $73.60   $73.60  
  Purchase #2 $88.47   4.607%   $92.5458   $92.55   $92.55   $92.50  
  Purchase #3 $239.46   11.348%   $266.6339   $266.63   $266.65   $266.60  
  Purchase #4 $61.45   10.393%   $67.8365   $67.84   $67.85   $67.80  
  Purchase #5 $221.83   6.231%   $235.6522   $235.65   $235.65   $235.70  
  Purchase #6 $70.74   7.531%   $76.0674   $76.07   $76.05   $76.10  
  Purchase #7 $6.86   7.492%   $7.374   $7.37   $7.35   $7.40  
  7 purchase totals = $754.07       $819.7074   $819.71   $819.70   $819.70