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 $183.25   6.116%   $194.4576   $194.46   $194.45   $194.50  
  Purchase #2 $246.78   9.813%   $270.9965   $271.00   $271.00   $271.00  
  Purchase #3 $197.57   8.493%   $214.3496   $214.35   $214.35   $214.30  
  Purchase #4 $109.27   4.393%   $114.0702   $114.07   $114.05   $114.10  
  Purchase #5 $46.69   4.600%   $48.8377   $48.84   $48.85   $48.80  
  Purchase #6 $246.93   7.645%   $265.8078   $265.81   $265.80   $265.80  
  Purchase #7 $136.75   11.716%   $152.7716   $152.77   $152.75   $152.80  
  7 purchase totals = $1,167.24       $1,261.2910   $1,261.30   $1,261.25   $1,261.30