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 $250.54   9.368%   $274.0106   $274.01   $274.00   $274.00  
  Purchase #2 $71.47   4.861%   $74.9442   $74.94   $74.95   $74.90  
  Purchase #3 $170.36   8.116%   $184.1864   $184.19   $184.20   $184.20  
  Purchase #4 $164.87   6.635%   $175.8091   $175.81   $175.80   $175.80  
  Purchase #5 $128.59   5.735%   $135.9646   $135.96   $135.95   $136.00  
  Purchase #6 $200.89   3.757%   $208.4374   $208.44   $208.45   $208.40  
  Purchase #7 $8.50   13.686%   $9.6633   $9.66   $9.65   $9.70  
  7 purchase totals = $995.22       $1,063.0156   $1,063.01   $1,063.00   $1,063.00