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	$99.35	12.206%	$111.4767	$111.48	$111.50	$111.50
Purchase #2	$146.39	13.206%	$165.7223	$165.72	$165.70	$165.70
Purchase #3	$196.39	9.846%	$215.7266	$215.73	$215.75	$215.70
Purchase #4	$172.91	11.627%	$193.0142	$193.01	$193.00	$193.00
Purchase #5	$52.41	6.303%	$55.7134	$55.71	$55.70	$55.70
Purchase #6	$239.83	13.435%	$272.0512	$272.05	$272.05	$272.10
Purchase #7	$12.44	9.324%	$13.5999	$13.60	$13.60	$13.60
7 purchase totals =	$919.72		$1,027.3043	$1,027.30	$1,027.30	$1,027.30