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 $153.83   13.305%   $174.2971   $174.30   $174.30   $174.30  
  Purchase #2 $186.62   4.298%   $194.6409   $194.64   $194.65   $194.60  
  Purchase #3 $70.71   6.751%   $75.4836   $75.48   $75.50   $75.50  
  Purchase #4 $22.93   13.834%   $26.1021   $26.10   $26.10   $26.10  
  Purchase #5 $197.48   11.705%   $220.595   $220.60   $220.60   $220.60  
  Purchase #6 $13.99   6.287%   $14.8696   $14.87   $14.85   $14.90  
  Purchase #7 $109.97   5.202%   $115.6906   $115.69   $115.70   $115.70  
  7 purchase totals = $755.53       $821.6789   $821.68   $821.70   $821.70