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 $23.60   12.430%   $26.5335   $26.53   $26.55   $26.50  
  Purchase #2 $120.43   13.690%   $136.9169   $136.92   $136.90   $136.90  
  Purchase #3 $21.94   11.637%   $24.4932   $24.49   $24.50   $24.50  
  Purchase #4 $58.98   13.528%   $66.9588   $66.96   $66.95   $67.00  
  Purchase #5 $212.92   3.739%   $220.8811   $220.88   $220.90   $220.90  
  Purchase #6 $162.82   7.284%   $174.6798   $174.68   $174.70   $174.70  
  Purchase #7 $76.70   5.620%   $81.0105   $81.01   $81.00   $81.00  
  7 purchase totals = $677.39       $731.4738   $731.47   $731.50   $731.50