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 $177.64   13.298%   $201.2626   $201.26   $201.25   $201.30  
  Purchase #2 $22.58   10.227%   $24.8893   $24.89   $24.90   $24.90  
  Purchase #3 $93.86   5.318%   $98.8515   $98.85   $98.85   $98.90  
  Purchase #4 $171.98   13.360%   $194.9565   $194.96   $194.95   $195.00  
  Purchase #5 $56.58   8.458%   $61.3655   $61.37   $61.35   $61.40  
  Purchase #6 $57.67   4.143%   $60.0593   $60.06   $60.05   $60.10  
  Purchase #7 $72.32   11.376%   $80.5471   $80.55   $80.55   $80.50  
  7 purchase totals = $652.63       $721.9318   $721.94   $721.90   $722.10