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 $249.38   7.365%   $267.7468   $267.75   $267.75   $267.70  
  Purchase #2 $134.61   7.497%   $144.7017   $144.70   $144.70   $144.70  
  Purchase #3 $138.26   11.141%   $153.6635   $153.66   $153.65   $153.70  
  Purchase #4 $182.47   7.868%   $196.8267   $196.83   $196.85   $196.80  
  Purchase #5 $242.99   11.553%   $271.0626   $271.06   $271.05   $271.10  
  Purchase #6 $111.83   6.128%   $118.6829   $118.68   $118.70   $118.70  
  Purchase #7 $39.54   6.112%   $41.9567   $41.96   $41.95   $42.00  
  7 purchase totals = $1,099.08       $1,194.6409   $1,194.64   $1,194.65   $1,194.70