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 $161.55   12.131%   $181.1476   $181.15   $181.15   $181.10  
  Purchase #2 $168.75   9.565%   $184.8909   $184.89   $184.90   $184.90  
  Purchase #3 $241.58   3.456%   $249.929   $249.93   $249.95   $249.90  
  Purchase #4 $44.69   5.506%   $47.1506   $47.15   $47.15   $47.20  
  Purchase #5 $231.89   13.522%   $263.2462   $263.25   $263.25   $263.20  
  Purchase #6 $112.29   10.869%   $124.4948   $124.49   $124.50   $124.50  
  Purchase #7 $207.89   6.121%   $220.6149   $220.61   $220.60   $220.60  
  7 purchase totals = $1,168.64       $1,271.4740   $1,271.47   $1,271.50   $1,271.40