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 $207.82   9.789%   $228.1635   $228.16   $228.15   $228.20  
  Purchase #2 $173.44   5.468%   $182.9237   $182.92   $182.90   $182.90  
  Purchase #3 $213.58   12.649%   $240.5957   $240.60   $240.60   $240.60  
  Purchase #4 $249.60   3.659%   $258.7329   $258.73   $258.75   $258.70  
  Purchase #5 $23.97   12.651%   $27.0024   $27.00   $27.00   $27.00  
  Purchase #6 $179.35   9.766%   $196.8653   $196.87   $196.85   $196.90  
  Purchase #7 $129.43   3.783%   $134.3263   $134.33   $134.35   $134.30  
  7 purchase totals = $1,177.19       $1,268.6098   $1,268.61   $1,268.60   $1,268.60