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 $61.54   13.632%   $69.9291   $69.93   $69.95   $69.90  
  Purchase #2 $49.80   4.522%   $52.052   $52.05   $52.05   $52.10  
  Purchase #3 $124.33   7.442%   $133.5826   $133.58   $133.60   $133.60  
  Purchase #4 $97.93   3.657%   $101.5113   $101.51   $101.50   $101.50  
  Purchase #5 $41.49   6.816%   $44.318   $44.32   $44.30   $44.30  
  Purchase #6 $44.61   5.262%   $46.9574   $46.96   $46.95   $47.00  
  Purchase #7 $54.51   11.812%   $60.9487   $60.95   $60.95   $60.90  
  7 purchase totals = $474.21       $509.2991   $509.30   $509.30   $509.30