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	$11.72	11.349%	$13.0501	$13.05	$13.05	$13.10
Purchase #2	$158.96	5.621%	$167.8951	$167.90	$167.90	$167.90
Purchase #3	$88.76	9.807%	$97.4647	$97.46	$97.45	$97.50
Purchase #4	$54.25	11.410%	$60.4399	$60.44	$60.45	$60.40
Purchase #5	$153.81	12.687%	$173.3239	$173.32	$173.30	$173.30
Purchase #6	$109.74	8.300%	$118.8484	$118.85	$118.85	$118.80
Purchase #7	$52.94	11.671%	$59.1186	$59.12	$59.10	$59.10
7 purchase totals =	$630.18		$690.1407	$690.14	$690.10	$690.10