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	$21.48	9.631%	$23.5487	$23.55	$23.55	$23.50
Purchase #2	$214.65	13.471%	$243.5655	$243.57	$243.55	$243.60
Purchase #3	$208.58	3.401%	$215.6738	$215.67	$215.65	$215.70
Purchase #4	$28.41	10.767%	$31.4689	$31.47	$31.45	$31.50
Purchase #5	$89.31	3.384%	$92.3323	$92.33	$92.35	$92.30
Purchase #6	$35.81	8.769%	$38.9502	$38.95	$38.95	$39.00
Purchase #7	$100.45	8.852%	$109.3418	$109.34	$109.35	$109.30
7 purchase totals =	$698.69		$754.8812	$754.88	$754.85	$754.90