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 $24.49   9.603%   $26.8418   $26.84   $26.85   $26.80  
  Purchase #2 $106.51   7.242%   $114.2235   $114.22   $114.20   $114.20  
  Purchase #3 $204.72   8.848%   $222.8336   $222.83   $222.85   $222.80  
  Purchase #4 $145.30   6.447%   $154.6675   $154.67   $154.65   $154.70  
  Purchase #5 $194.36   3.354%   $200.8788   $200.88   $200.90   $200.90  
  Purchase #6 $182.60   3.310%   $188.6441   $188.64   $188.65   $188.60  
  Purchase #7 $41.78   4.783%   $43.7783   $43.78   $43.80   $43.80  
  7 purchase totals = $899.76       $951.8676   $951.86   $951.90   $951.80