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 $50.61   3.241%   $52.2503   $52.25   $52.25   $52.30  
  Purchase #2 $215.89   7.196%   $231.4254   $231.43   $231.45   $231.40  
  Purchase #3 $233.99   9.541%   $256.315   $256.32   $256.30   $256.30  
  Purchase #4 $57.96   3.441%   $59.9544   $59.95   $59.95   $60.00  
  Purchase #5 $5.72   12.608%   $6.4412   $6.44   $6.45   $6.40  
  Purchase #6 $169.42   4.197%   $176.5306   $176.53   $176.55   $176.50  
  Purchase #7 $68.77   6.647%   $73.3411   $73.34   $73.35   $73.30  
  7 purchase totals = $802.36       $856.2580   $856.26   $856.30   $856.20