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	$214.79	11.525%	$239.5445	$239.54	$239.55	$239.50
Purchase #2	$169.77	13.188%	$192.1593	$192.16	$192.15	$192.20
Purchase #3	$134.40	12.610%	$151.3478	$151.35	$151.35	$151.30
Purchase #4	$58.92	11.832%	$65.8914	$65.89	$65.90	$65.90
Purchase #5	$152.41	12.342%	$171.2204	$171.22	$171.20	$171.20
Purchase #6	$96.51	10.472%	$106.6165	$106.62	$106.60	$106.60
Purchase #7	$212.53	12.354%	$238.786	$238.79	$238.80	$238.80
7 purchase totals =	$1,039.33		$1,165.5659	$1,165.57	$1,165.55	$1,165.50