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 $236.41   12.326%   $265.5499   $265.55   $265.55   $265.50  
  Purchase #2 $245.83   8.862%   $267.6155   $267.62   $267.60   $267.60  
  Purchase #3 $41.76   12.784%   $47.0986   $47.10   $47.10   $47.10  
  Purchase #4 $29.39   7.495%   $31.5928   $31.59   $31.60   $31.60  
  Purchase #5 $153.86   6.118%   $163.2732   $163.27   $163.25   $163.30  
  Purchase #6 $231.72   10.209%   $255.3763   $255.38   $255.40   $255.40  
  Purchase #7 $183.68   9.485%   $201.102   $201.10   $201.10   $201.10  
  7 purchase totals = $1,122.65       $1,231.6083   $1,231.61   $1,231.60   $1,231.60