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 $142.47   13.408%   $161.5724   $161.57   $161.55   $161.60  
  Purchase #2 $35.28   4.564%   $36.8902   $36.89   $36.90   $36.90  
  Purchase #3 $95.59   13.548%   $108.5405   $108.54   $108.55   $108.50  
  Purchase #4 $201.66   3.455%   $208.6274   $208.63   $208.65   $208.60  
  Purchase #5 $171.56   3.708%   $177.9214   $177.92   $177.90   $177.90  
  Purchase #6 $35.30   8.447%   $38.2818   $38.28   $38.30   $38.30  
  Purchase #7 $113.33   5.304%   $119.341   $119.34   $119.35   $119.30  
  7 purchase totals = $795.19       $851.1747   $851.17   $851.20   $851.10