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	$53.52	7.853%	$57.7229	$57.72	$57.70	$57.70
Purchase #2	$59.39	11.521%	$66.2323	$66.23	$66.25	$66.20
Purchase #3	$145.36	9.797%	$159.6009	$159.60	$159.60	$159.60
Purchase #4	$153.42	7.477%	$164.8912	$164.89	$164.90	$164.90
Purchase #5	$170.25	8.660%	$184.9937	$184.99	$185.00	$185.00
Purchase #6	$83.78	6.360%	$89.1084	$89.11	$89.10	$89.10
Purchase #7	$5.84	12.345%	$6.5609	$6.56	$6.55	$6.60
7 purchase totals =	$671.56		$729.1103	$729.10	$729.10	$729.10