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 $201.51   6.788%   $215.1885   $215.19   $215.20   $215.20  
  Purchase #2 $58.66   11.649%   $65.4933   $65.49   $65.50   $65.50  
  Purchase #3 $48.33   9.182%   $52.7677   $52.77   $52.75   $52.80  
  Purchase #4 $161.39   3.825%   $167.5632   $167.56   $167.55   $167.60  
  Purchase #5 $146.66   5.371%   $154.5371   $154.54   $154.55   $154.50  
  Purchase #6 $24.64   7.599%   $26.5124   $26.51   $26.50   $26.50  
  Purchase #7 $98.54   13.772%   $112.1109   $112.11   $112.10   $112.10  
  7 purchase totals = $739.73       $794.1731   $794.17   $794.15   $794.20