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 $67.26   13.289%   $76.1982   $76.20   $76.20   $76.20  
  Purchase #2 $62.76   12.699%   $70.7299   $70.73   $70.75   $70.70  
  Purchase #3 $234.45   5.125%   $246.4656   $246.47   $246.45   $246.50  
  Purchase #4 $127.76   3.667%   $132.445   $132.45   $132.45   $132.40  
  Purchase #5 $44.50   9.312%   $48.6438   $48.64   $48.65   $48.60  
  Purchase #6 $182.37   5.579%   $192.5444   $192.54   $192.55   $192.50  
  Purchase #7 $56.57   3.140%   $58.3463   $58.35   $58.35   $58.30  
  7 purchase totals = $775.67       $825.3732   $825.38   $825.40   $825.20