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	$243.52	3.161%	$251.2177	$251.22	$251.20	$251.20
Purchase #2	$33.70	4.651%	$35.2674	$35.27	$35.25	$35.30
Purchase #3	$230.59	6.690%	$246.0165	$246.02	$246.00	$246.00
Purchase #4	$101.73	6.618%	$108.4625	$108.46	$108.45	$108.50
Purchase #5	$174.91	11.194%	$194.4894	$194.49	$194.50	$194.50
Purchase #6	$149.60	9.856%	$164.3446	$164.34	$164.35	$164.30
Purchase #7	$100.61	4.476%	$105.1133	$105.11	$105.10	$105.10
7 purchase totals =	$1,034.66		$1,104.9114	$1,104.91	$1,104.85	$1,104.90