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 $77.38   11.446%   $86.2369   $86.24   $86.25   $86.20  
  Purchase #2 $101.91   10.390%   $112.4984   $112.50   $112.50   $112.50  
  Purchase #3 $243.66   7.799%   $262.663   $262.66   $262.65   $262.70  
  Purchase #4 $55.37   12.556%   $62.3223   $62.32   $62.30   $62.30  
  Purchase #5 $236.57   12.569%   $266.3045   $266.30   $266.30   $266.30  
  Purchase #6 $153.89   11.211%   $171.1426   $171.14   $171.15   $171.10  
  Purchase #7 $214.98   5.234%   $226.2321   $226.23   $226.25   $226.20  
  7 purchase totals = $1,083.76       $1,187.3998   $1,187.39   $1,187.40   $1,187.30