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 $206.68   9.252%   $225.802   $225.80   $225.80   $225.80  
  Purchase #2 $82.33   3.164%   $84.9349   $84.93   $84.95   $84.90  
  Purchase #3 $115.48   3.178%   $119.15   $119.15   $119.15   $119.20  
  Purchase #4 $221.42   8.234%   $239.6517   $239.65   $239.65   $239.70  
  Purchase #5 $248.83   10.595%   $275.1935   $275.19   $275.20   $275.20  
  Purchase #6 $80.34   6.168%   $85.2954   $85.30   $85.30   $85.30  
  Purchase #7 $34.47   7.549%   $37.0721   $37.07   $37.05   $37.10  
  7 purchase totals = $989.55       $1,067.0996   $1,067.09   $1,067.10   $1,067.20