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 $38.40   6.733%   $40.9855   $40.99   $41.00   $41.00  
  Purchase #2 $159.48   4.867%   $167.2419   $167.24   $167.25   $167.20  
  Purchase #3 $169.88   8.295%   $183.9715   $183.97   $183.95   $184.00  
  Purchase #4 $244.47   9.201%   $266.9637   $266.96   $266.95   $267.00  
  Purchase #5 $248.36   7.612%   $267.2652   $267.27   $267.25   $267.30  
  Purchase #6 $249.25   13.373%   $282.5822   $282.58   $282.60   $282.60  
  Purchase #7 $117.61   4.544%   $122.9542   $122.95   $122.95   $123.00  
  7 purchase totals = $1,227.45       $1,331.9642   $1,331.96   $1,331.95   $1,332.10