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 $61.70   3.644%   $63.9483   $63.95   $63.95   $63.90  
  Purchase #2 $220.54   12.724%   $248.6015   $248.60   $248.60   $248.60  
  Purchase #3 $16.49   12.602%   $18.5681   $18.57   $18.55   $18.60  
  Purchase #4 $190.33   11.256%   $211.7535   $211.75   $211.75   $211.80  
  Purchase #5 $97.54   7.448%   $104.8048   $104.80   $104.80   $104.80  
  Purchase #6 $145.36   11.507%   $162.0866   $162.09   $162.10   $162.10  
  Purchase #7 $170.55   4.138%   $177.6074   $177.61   $177.60   $177.60  
  7 purchase totals = $902.51       $987.3702   $987.37   $987.35   $987.40