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	$167.46	7.144%	$179.4233	$179.42	$179.40	$179.40
Purchase #2	$196.46	8.544%	$213.2455	$213.25	$213.25	$213.20
Purchase #3	$12.63	6.624%	$13.4666	$13.47	$13.45	$13.50
Purchase #4	$13.62	12.751%	$15.3567	$15.36	$15.35	$15.40
Purchase #5	$46.41	13.337%	$52.5997	$52.60	$52.60	$52.60
Purchase #6	$60.68	9.559%	$66.4804	$66.48	$66.50	$66.50
Purchase #7	$39.53	7.865%	$42.639	$42.64	$42.65	$42.60
7 purchase totals =	$536.79		$583.2112	$583.22	$583.20	$583.20