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 $116.34   8.530%   $126.2638   $126.26   $126.25   $126.30  
  Purchase #2 $173.47   12.326%   $194.8519   $194.85   $194.85   $194.90  
  Purchase #3 $97.61   12.285%   $109.6014   $109.60   $109.60   $109.60  
  Purchase #4 $120.68   8.475%   $130.9076   $130.91   $130.90   $130.90  
  Purchase #5 $200.66   8.192%   $217.0981   $217.10   $217.10   $217.10  
  Purchase #6 $78.58   10.203%   $86.5975   $86.60   $86.60   $86.60  
  Purchase #7 $190.45   8.307%   $206.2707   $206.27   $206.25   $206.30  
  7 purchase totals = $977.79       $1,071.5910   $1,071.59   $1,071.55   $1,071.70