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	$75.69	4.123%	$78.8107	$78.81	$78.80	$78.80
Purchase #2	$173.80	10.704%	$192.4036	$192.40	$192.40	$192.40
Purchase #3	$124.86	4.452%	$130.4188	$130.42	$130.40	$130.40
Purchase #4	$223.77	11.321%	$249.103	$249.10	$249.10	$249.10
Purchase #5	$27.58	7.728%	$29.7114	$29.71	$29.70	$29.70
Purchase #6	$226.34	9.809%	$248.5417	$248.54	$248.55	$248.50
Purchase #7	$78.67	6.616%	$83.8748	$83.87	$83.85	$83.90
7 purchase totals =	$930.71		$1,012.8640	$1,012.85	$1,012.80	$1,012.80