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 $64.87   13.137%   $73.392   $73.39   $73.40   $73.40  
  Purchase #2 $248.48   11.151%   $276.188   $276.19   $276.20   $276.20  
  Purchase #3 $20.91   8.274%   $22.6401   $22.64   $22.65   $22.60  
  Purchase #4 $52.76   11.543%   $58.8501   $58.85   $58.85   $58.90  
  Purchase #5 $85.32   10.359%   $94.1583   $94.16   $94.15   $94.20  
  Purchase #6 $47.87   13.439%   $54.3032   $54.30   $54.30   $54.30  
  Purchase #7 $148.36   10.523%   $163.9719   $163.97   $163.95   $164.00  
  7 purchase totals = $668.57       $743.5036   $743.50   $743.50   $743.60