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	$32.79	5.163%	$34.4829	$34.48	$34.50	$34.50
Purchase #2	$140.65	4.194%	$146.5489	$146.55	$146.55	$146.50
Purchase #3	$169.43	5.695%	$179.079	$179.08	$179.10	$179.10
Purchase #4	$36.44	8.171%	$39.4175	$39.42	$39.40	$39.40
Purchase #5	$228.94	4.191%	$238.5349	$238.53	$238.55	$238.50
Purchase #6	$99.99	11.244%	$111.2329	$111.23	$111.25	$111.20
Purchase #7	$221.64	6.566%	$236.1929	$236.19	$236.20	$236.20
7 purchase totals =	$929.88		$985.4890	$985.48	$985.55	$985.40