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	$82.58	8.274%	$89.4127	$89.41	$89.40	$89.40
Purchase #2	$115.36	12.825%	$130.1549	$130.15	$130.15	$130.20
Purchase #3	$247.44	7.490%	$265.9733	$265.97	$265.95	$266.00
Purchase #4	$142.59	13.178%	$161.3805	$161.38	$161.40	$161.40
Purchase #5	$177.69	7.613%	$191.2175	$191.22	$191.20	$191.20
Purchase #6	$120.74	4.719%	$126.4377	$126.44	$126.45	$126.40
Purchase #7	$162.64	10.563%	$179.8197	$179.82	$179.80	$179.80
7 purchase totals =	$1,049.04		$1,144.3963	$1,144.39	$1,144.35	$1,144.40