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 $176.59   11.195%   $196.3593   $196.36   $196.35   $196.40  
  Purchase #2 $173.40   6.852%   $185.2814   $185.28   $185.30   $185.30  
  Purchase #3 $248.76   9.609%   $272.6633   $272.66   $272.65   $272.70  
  Purchase #4 $127.49   5.312%   $134.2623   $134.26   $134.25   $134.30  
  Purchase #5 $104.71   8.753%   $113.8753   $113.88   $113.90   $113.90  
  Purchase #6 $189.64   4.245%   $197.6902   $197.69   $197.70   $197.70  
  Purchase #7 $250.94   6.795%   $267.9914   $267.99   $268.00   $268.00  
  7 purchase totals = $1,271.53       $1,368.1232   $1,368.12   $1,368.15   $1,368.30