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	$165.44	12.656%	$186.3781	$186.38	$186.40	$186.40
Purchase #2	$118.53	8.351%	$128.4284	$128.43	$128.45	$128.40
Purchase #3	$214.50	7.268%	$230.0899	$230.09	$230.10	$230.10
Purchase #4	$119.73	11.405%	$133.3852	$133.39	$133.40	$133.40
Purchase #5	$33.66	5.396%	$35.4763	$35.48	$35.50	$35.50
Purchase #6	$37.78	11.415%	$42.0926	$42.09	$42.10	$42.10
Purchase #7	$39.97	13.420%	$45.334	$45.33	$45.35	$45.30
7 purchase totals =	$729.61		$801.1845	$801.19	$801.30	$801.20