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	$244.35	13.854%	$278.2022	$278.20	$278.20	$278.20
Purchase #2	$88.92	12.339%	$99.8918	$99.89	$99.90	$99.90
Purchase #3	$35.98	12.157%	$40.3541	$40.35	$40.35	$40.40
Purchase #4	$57.83	3.469%	$59.8361	$59.84	$59.85	$59.80
Purchase #5	$141.29	3.864%	$146.7494	$146.75	$146.75	$146.70
Purchase #6	$77.70	13.542%	$88.2221	$88.22	$88.20	$88.20
Purchase #7	$119.45	11.492%	$133.1772	$133.18	$133.20	$133.20
7 purchase totals =	$765.52		$846.4329	$846.43	$846.45	$846.40