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	$97.78	4.112%	$101.8007	$101.80	$101.80	$101.80
Purchase #2	$53.94	9.629%	$59.1339	$59.13	$59.15	$59.10
Purchase #3	$46.26	10.586%	$51.1571	$51.16	$51.15	$51.20
Purchase #4	$158.82	9.510%	$173.9238	$173.92	$173.90	$173.90
Purchase #5	$239.80	13.848%	$273.0075	$273.01	$273.00	$273.00
Purchase #6	$31.54	11.233%	$35.0829	$35.08	$35.10	$35.10
Purchase #7	$144.75	11.517%	$161.4209	$161.42	$161.40	$161.40
7 purchase totals =	$772.89		$855.5268	$855.52	$855.50	$855.50