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 $23.93   8.597%   $25.9873   $25.99   $26.00   $26.00  
  Purchase #2 $43.88   13.213%   $49.6779   $49.68   $49.70   $49.70  
  Purchase #3 $82.87   3.757%   $85.9834   $85.98   $86.00   $86.00  
  Purchase #4 $173.85   12.139%   $194.9537   $194.95   $194.95   $195.00  
  Purchase #5 $151.74   8.469%   $164.5909   $164.59   $164.60   $164.60  
  Purchase #6 $214.65   4.356%   $224.0002   $224.00   $224.00   $224.00  
  Purchase #7 $96.45   10.451%   $106.53   $106.53   $106.55   $106.50  
  7 purchase totals = $787.37       $851.7234   $851.72   $851.80   $851.80