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 $22.96   13.470%   $26.0527   $26.05   $26.05   $26.10  
  Purchase #2 $108.83   10.844%   $120.6315   $120.63   $120.65   $120.60  
  Purchase #3 $164.89   8.554%   $178.9947   $178.99   $179.00   $179.00  
  Purchase #4 $148.48   12.452%   $166.9687   $166.97   $166.95   $167.00  
  Purchase #5 $125.71   3.832%   $130.5272   $130.53   $130.55   $130.50  
  Purchase #6 $91.42   7.365%   $98.1531   $98.15   $98.15   $98.20  
  Purchase #7 $146.72   5.700%   $155.083   $155.08   $155.10   $155.10  
  7 purchase totals = $809.01       $876.4109   $876.40   $876.45   $876.50