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 $224.54   10.697%   $248.559   $248.56   $248.55   $248.60  
  Purchase #2 $169.80   3.769%   $176.1998   $176.20   $176.20   $176.20  
  Purchase #3 $141.75   11.437%   $157.9619   $157.96   $157.95   $158.00  
  Purchase #4 $111.27   10.157%   $122.5717   $122.57   $122.55   $122.60  
  Purchase #5 $106.76   10.586%   $118.0616   $118.06   $118.05   $118.10  
  Purchase #6 $187.68   4.466%   $196.0618   $196.06   $196.05   $196.10  
  Purchase #7 $235.66   7.601%   $253.5725   $253.57   $253.55   $253.60  
  7 purchase totals = $1,177.46       $1,272.9883   $1,272.98   $1,272.90   $1,273.20