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	$26.31	4.488%	$27.4908	$27.49	$27.50	$27.50
Purchase #2	$159.80	3.818%	$165.9012	$165.90	$165.90	$165.90
Purchase #3	$62.87	5.676%	$66.4385	$66.44	$66.45	$66.40
Purchase #4	$173.61	3.531%	$179.7402	$179.74	$179.75	$179.70
Purchase #5	$220.74	11.605%	$246.3569	$246.36	$246.35	$246.40
Purchase #6	$40.97	11.797%	$45.8032	$45.80	$45.80	$45.80
Purchase #7	$115.86	9.733%	$127.1367	$127.14	$127.15	$127.10
7 purchase totals =	$800.16		$858.8675	$858.87	$858.90	$858.80