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 $206.31   12.407%   $231.9069   $231.91   $231.90   $231.90  
  Purchase #2 $13.62   8.316%   $14.7526   $14.75   $14.75   $14.80  
  Purchase #3 $194.71   13.297%   $220.6006   $220.60   $220.60   $220.60  
  Purchase #4 $174.42   10.563%   $192.844   $192.84   $192.85   $192.80  
  Purchase #5 $111.68   10.333%   $123.2199   $123.22   $123.20   $123.20  
  Purchase #6 $240.38   9.329%   $262.8051   $262.81   $262.80   $262.80  
  Purchase #7 $196.47   3.581%   $203.5056   $203.51   $203.50   $203.50  
  7 purchase totals = $1,137.59       $1,249.6347   $1,249.64   $1,249.60   $1,249.60