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	$229.78	11.127%	$255.3476	$255.35	$255.35	$255.30
Purchase #2	$129.61	13.495%	$147.1009	$147.10	$147.10	$147.10
Purchase #3	$218.44	5.139%	$229.6656	$229.67	$229.65	$229.70
Purchase #4	$32.76	13.813%	$37.2851	$37.29	$37.30	$37.30
Purchase #5	$230.99	4.769%	$242.0059	$242.01	$242.00	$242.00
Purchase #6	$159.93	8.442%	$173.4313	$173.43	$173.45	$173.40
Purchase #7	$125.59	11.739%	$140.333	$140.33	$140.35	$140.30
7 purchase totals =	$1,127.10		$1,225.1694	$1,225.18	$1,225.20	$1,225.10