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 $228.99   13.500%   $259.9037   $259.90   $259.90   $259.90  
  Purchase #2 $33.93   6.421%   $36.1086   $36.11   $36.10   $36.10  
  Purchase #3 $166.61   11.608%   $185.9501   $185.95   $185.95   $186.00  
  Purchase #4 $201.88   6.145%   $214.2855   $214.29   $214.30   $214.30  
  Purchase #5 $197.93   8.735%   $215.2192   $215.22   $215.20   $215.20  
  Purchase #6 $218.30   9.836%   $239.772   $239.77   $239.75   $239.80  
  Purchase #7 $216.95   6.661%   $231.401   $231.40   $231.40   $231.40  
  7 purchase totals = $1,264.59       $1,382.6401   $1,382.64   $1,382.60   $1,382.70