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	$74.68	11.667%	$83.3929	$83.39	$83.40	$83.40
Purchase #2	$173.37	7.727%	$186.7663	$186.77	$186.75	$186.80
Purchase #3	$45.54	12.656%	$51.3035	$51.30	$51.30	$51.30
Purchase #4	$139.89	13.293%	$158.4856	$158.49	$158.50	$158.50
Purchase #5	$99.37	3.377%	$102.7257	$102.73	$102.75	$102.70
Purchase #6	$105.70	12.366%	$118.7709	$118.77	$118.75	$118.80
Purchase #7	$101.91	9.148%	$111.2327	$111.23	$111.25	$111.20
7 purchase totals =	$740.46		$812.6776	$812.68	$812.70	$812.70