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 $14.34   11.857%   $16.0403   $16.04   $16.05   $16.00  
  Purchase #2 $248.53   12.463%   $279.5043   $279.50   $279.50   $279.50  
  Purchase #3 $113.70   12.225%   $127.5998   $127.60   $127.60   $127.60  
  Purchase #4 $192.60   7.267%   $206.5962   $206.60   $206.60   $206.60  
  Purchase #5 $249.67   11.732%   $278.9613   $278.96   $278.95   $279.00  
  Purchase #6 $211.51   6.620%   $225.512   $225.51   $225.50   $225.50  
  Purchase #7 $16.90   13.246%   $19.1386   $19.14   $19.15   $19.10  
  7 purchase totals = $1,047.25       $1,153.3525   $1,153.35   $1,153.35   $1,153.30