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	$108.59	12.673%	$122.3516	$122.35	$122.35	$122.40
Purchase #2	$111.73	13.710%	$127.0482	$127.05	$127.05	$127.00
Purchase #3	$233.86	13.288%	$264.9353	$264.94	$264.95	$264.90
Purchase #4	$92.88	3.830%	$96.4373	$96.44	$96.45	$96.40
Purchase #5	$18.80	4.325%	$19.6131	$19.61	$19.60	$19.60
Purchase #6	$55.53	6.747%	$59.2766	$59.28	$59.30	$59.30
Purchase #7	$38.42	11.228%	$42.7338	$42.73	$42.75	$42.70
7 purchase totals =	$659.81		$732.3959	$732.40	$732.45	$732.30