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	$100.85	8.372%	$109.2932	$109.29	$109.30	$109.30
Purchase #2	$62.37	3.190%	$64.3596	$64.36	$64.35	$64.40
Purchase #3	$134.43	13.529%	$152.617	$152.62	$152.60	$152.60
Purchase #4	$113.91	11.711%	$127.25	$127.25	$127.25	$127.30
Purchase #5	$54.67	6.649%	$58.305	$58.31	$58.30	$58.30
Purchase #6	$147.88	4.436%	$154.44	$154.44	$154.45	$154.40
Purchase #7	$10.83	8.130%	$11.7105	$11.71	$11.70	$11.70
7 purchase totals =	$624.94		$677.9753	$677.98	$677.95	$678.00