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 $86.66   9.149%   $94.5885   $94.59   $94.60   $94.60  
  Purchase #2 $134.56   7.665%   $144.874   $144.87   $144.85   $144.90  
  Purchase #3 $244.56   8.344%   $264.9661   $264.97   $264.95   $265.00  
  Purchase #4 $145.47   12.680%   $163.9156   $163.92   $163.90   $163.90  
  Purchase #5 $206.58   13.695%   $234.8711   $234.87   $234.85   $234.90  
  Purchase #6 $240.43   9.211%   $262.576   $262.58   $262.60   $262.60  
  Purchase #7 $155.83   13.502%   $176.8702   $176.87   $176.85   $176.90  
  7 purchase totals = $1,214.09       $1,342.6615   $1,342.67   $1,342.60   $1,342.80