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 $162.48   13.256%   $184.0183   $184.02   $184.00   $184.00  
  Purchase #2 $59.47   4.174%   $61.9523   $61.95   $61.95   $62.00  
  Purchase #3 $121.55   3.635%   $125.9683   $125.97   $125.95   $126.00  
  Purchase #4 $74.76   7.356%   $80.2593   $80.26   $80.25   $80.30  
  Purchase #5 $6.77   13.209%   $7.6642   $7.66   $7.65   $7.70  
  Purchase #6 $86.41   13.306%   $97.9077   $97.91   $97.90   $97.90  
  Purchase #7 $53.26   13.296%   $60.3414   $60.34   $60.35   $60.30  
  7 purchase totals = $564.70       $618.1115   $618.11   $618.05   $618.20