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	$123.40	3.285%	$127.4537	$127.45	$127.45	$127.50
Purchase #2	$81.96	7.265%	$87.9144	$87.91	$87.90	$87.90
Purchase #3	$184.64	5.268%	$194.3668	$194.37	$194.35	$194.40
Purchase #4	$165.51	3.490%	$171.2863	$171.29	$171.30	$171.30
Purchase #5	$47.68	3.864%	$49.5224	$49.52	$49.50	$49.50
Purchase #6	$97.91	13.860%	$111.4803	$111.48	$111.50	$111.50
Purchase #7	$115.97	5.448%	$122.288	$122.29	$122.30	$122.30
7 purchase totals =	$817.07		$864.3119	$864.31	$864.30	$864.40