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	$104.99	13.626%	$119.2959	$119.30	$119.30	$119.30
Purchase #2	$5.81	11.364%	$6.4702	$6.47	$6.45	$6.50
Purchase #3	$65.64	10.328%	$72.4193	$72.42	$72.40	$72.40
Purchase #4	$159.78	4.765%	$167.3935	$167.39	$167.40	$167.40
Purchase #5	$167.45	10.720%	$185.4006	$185.40	$185.40	$185.40
Purchase #6	$206.75	12.745%	$233.1003	$233.10	$233.10	$233.10
Purchase #7	$54.52	4.750%	$57.1097	$57.11	$57.10	$57.10
7 purchase totals =	$764.94		$841.1895	$841.19	$841.15	$841.20