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 $33.54   3.688%   $34.777   $34.78   $34.80   $34.80  
  Purchase #2 $69.68   3.130%   $71.861   $71.86   $71.85   $71.90  
  Purchase #3 $101.39   10.729%   $112.2681   $112.27   $112.25   $112.30  
  Purchase #4 $245.27   8.198%   $265.3772   $265.38   $265.40   $265.40  
  Purchase #5 $46.76   5.139%   $49.163   $49.16   $49.15   $49.20  
  Purchase #6 $8.55   6.498%   $9.1056   $9.11   $9.10   $9.10  
  Purchase #7 $171.90   4.133%   $179.0046   $179.00   $179.00   $179.00  
  7 purchase totals = $677.09       $721.5565   $721.56   $721.55   $721.70