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 $83.59   3.598%   $86.5976   $86.60   $86.60   $86.60  
  Purchase #2 $242.71   12.621%   $273.3424   $273.34   $273.35   $273.30  
  Purchase #3 $175.77   9.654%   $192.7388   $192.74   $192.75   $192.70  
  Purchase #4 $163.84   13.337%   $185.6913   $185.69   $185.70   $185.70  
  Purchase #5 $119.77   10.713%   $132.601   $132.60   $132.60   $132.60  
  Purchase #6 $16.41   6.667%   $17.5041   $17.50   $17.50   $17.50  
  Purchase #7 $66.65   10.321%   $73.5289   $73.53   $73.55   $73.50  
  7 purchase totals = $868.74       $962.0041   $962.00   $962.05   $961.90