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	$245.27	4.619%	$256.599	$256.60	$256.60	$256.60
Purchase #2	$236.63	11.153%	$263.0213	$263.02	$263.00	$263.00
Purchase #3	$45.95	9.432%	$50.284	$50.28	$50.30	$50.30
Purchase #4	$223.30	12.836%	$251.9628	$251.96	$251.95	$252.00
Purchase #5	$19.39	7.294%	$20.8043	$20.80	$20.80	$20.80
Purchase #6	$137.71	9.294%	$150.5088	$150.51	$150.50	$150.50
Purchase #7	$40.84	11.191%	$45.4104	$45.41	$45.40	$45.40
7 purchase totals =	$949.09		$1,038.5906	$1,038.58	$1,038.55	$1,038.60