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 $211.35   3.356%   $218.4429   $218.44   $218.45   $218.40  
  Purchase #2 $15.72   10.433%   $17.3601   $17.36   $17.35   $17.40  
  Purchase #3 $239.44   8.169%   $258.9999   $259.00   $259.00   $259.00  
  Purchase #4 $248.66   7.350%   $266.9365   $266.94   $266.95   $266.90  
  Purchase #5 $205.70   4.731%   $215.4317   $215.43   $215.45   $215.40  
  Purchase #6 $169.99   6.725%   $181.4218   $181.42   $181.40   $181.40  
  Purchase #7 $104.64   4.776%   $109.6376   $109.64   $109.65   $109.60  
  7 purchase totals = $1,195.50       $1,268.2305   $1,268.23   $1,268.25   $1,268.10