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 $62.35   6.661%   $66.5031   $66.50   $66.50   $66.50  
  Purchase #2 $120.37   3.782%   $124.9224   $124.92   $124.90   $124.90  
  Purchase #3 $193.96   10.797%   $214.9019   $214.90   $214.90   $214.90  
  Purchase #4 $66.88   7.413%   $71.8378   $71.84   $71.85   $71.80  
  Purchase #5 $228.92   4.444%   $239.0932   $239.09   $239.10   $239.10  
  Purchase #6 $76.32   6.177%   $81.0343   $81.03   $81.05   $81.00  
  Purchase #7 $117.97   6.253%   $125.3467   $125.35   $125.35   $125.30  
  7 purchase totals = $866.77       $923.6394   $923.63   $923.65   $923.50