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	$124.27	12.813%	$140.1927	$140.19	$140.20	$140.20
Purchase #2	$154.29	8.558%	$167.4941	$167.49	$167.50	$167.50
Purchase #3	$46.46	3.803%	$48.2269	$48.23	$48.25	$48.20
Purchase #4	$46.67	3.417%	$48.2647	$48.26	$48.25	$48.30
Purchase #5	$64.70	3.739%	$67.1191	$67.12	$67.10	$67.10
Purchase #6	$113.27	12.444%	$127.3653	$127.37	$127.35	$127.40
Purchase #7	$74.82	10.456%	$82.6432	$82.64	$82.65	$82.60
7 purchase totals =	$624.48		$681.3060	$681.30	$681.30	$681.30