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	$226.25	5.586%	$238.8883	$238.89	$238.90	$238.90
Purchase #2	$150.25	5.669%	$158.7677	$158.77	$158.75	$158.80
Purchase #3	$113.55	5.258%	$119.5205	$119.52	$119.50	$119.50
Purchase #4	$175.75	5.422%	$185.2792	$185.28	$185.30	$185.30
Purchase #5	$33.92	5.621%	$35.8266	$35.83	$35.85	$35.80
Purchase #6	$70.52	11.281%	$78.4754	$78.48	$78.50	$78.50
Purchase #7	$46.86	6.453%	$49.8839	$49.88	$49.90	$49.90
7 purchase totals =	$817.10		$866.6416	$866.65	$866.70	$866.70