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	$186.56	12.344%	$209.589	$209.59	$209.60	$209.60
Purchase #2	$147.37	7.324%	$158.1634	$158.16	$158.15	$158.20
Purchase #3	$147.42	11.471%	$164.3305	$164.33	$164.35	$164.30
Purchase #4	$19.84	10.243%	$21.8722	$21.87	$21.85	$21.90
Purchase #5	$52.30	4.819%	$54.8203	$54.82	$54.80	$54.80
Purchase #6	$149.43	6.839%	$159.6495	$159.65	$159.65	$159.60
Purchase #7	$67.56	8.106%	$73.0364	$73.04	$73.05	$73.00
7 purchase totals =	$770.48		$841.4613	$841.46	$841.45	$841.40