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 $239.53   11.734%   $267.6365   $267.64   $267.65   $267.60  
  Purchase #2 $111.69   13.853%   $127.1624   $127.16   $127.15   $127.20  
  Purchase #3 $161.34   12.592%   $181.6559   $181.66   $181.65   $181.70  
  Purchase #4 $63.87   7.594%   $68.7203   $68.72   $68.70   $68.70  
  Purchase #5 $106.64   11.857%   $119.2843   $119.28   $119.30   $119.30  
  Purchase #6 $186.90   7.679%   $201.2521   $201.25   $201.25   $201.30  
  Purchase #7 $250.93   8.128%   $271.3256   $271.33   $271.35   $271.30  
  7 purchase totals = $1,120.90       $1,237.0371   $1,237.04   $1,237.05   $1,237.10