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	$23.35	12.643%	$26.3021	$26.30	$26.30	$26.30
Purchase #2	$52.80	12.406%	$59.3504	$59.35	$59.35	$59.40
Purchase #3	$231.84	5.406%	$244.3733	$244.37	$244.35	$244.40
Purchase #4	$126.85	3.137%	$130.8293	$130.83	$130.85	$130.80
Purchase #5	$96.82	4.716%	$101.386	$101.39	$101.40	$101.40
Purchase #6	$171.30	4.786%	$179.4984	$179.50	$179.50	$179.50
Purchase #7	$35.99	10.397%	$39.7319	$39.73	$39.75	$39.70
7 purchase totals =	$738.95		$781.4714	$781.47	$781.50	$781.50