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 $244.88   6.624%   $261.1009   $261.10   $261.10   $261.10  
  Purchase #2 $250.77   10.199%   $276.346   $276.35   $276.35   $276.30  
  Purchase #3 $69.48   13.693%   $78.9939   $78.99   $79.00   $79.00  
  Purchase #4 $82.81   8.824%   $90.1172   $90.12   $90.10   $90.10  
  Purchase #5 $95.87   11.177%   $106.5854   $106.59   $106.60   $106.60  
  Purchase #6 $95.41   13.833%   $108.6081   $108.61   $108.60   $108.60  
  Purchase #7 $147.44   6.819%   $157.4939   $157.49   $157.50   $157.50  
  7 purchase totals = $986.66       $1,079.2454   $1,079.25   $1,079.25   $1,079.20