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 $240.64   8.541%   $261.1931   $261.19   $261.20   $261.20  
  Purchase #2 $168.78   13.743%   $191.9754   $191.98   $192.00   $192.00  
  Purchase #3 $120.81   5.570%   $127.5391   $127.54   $127.55   $127.50  
  Purchase #4 $90.92   3.727%   $94.3086   $94.31   $94.30   $94.30  
  Purchase #5 $127.61   7.187%   $136.7813   $136.78   $136.80   $136.80  
  Purchase #6 $72.38   9.388%   $79.175   $79.18   $79.20   $79.20  
  Purchase #7 $178.54   7.120%   $191.252   $191.25   $191.25   $191.30  
  7 purchase totals = $999.68       $1,082.2245   $1,082.23   $1,082.30   $1,082.30