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	$167.88	10.556%	$185.6014	$185.60	$185.60	$185.60
Purchase #2	$229.41	3.797%	$238.1207	$238.12	$238.10	$238.10
Purchase #3	$219.37	6.377%	$233.3592	$233.36	$233.35	$233.40
Purchase #4	$180.91	3.391%	$187.0447	$187.04	$187.05	$187.00
Purchase #5	$118.39	7.727%	$127.538	$127.54	$127.55	$127.50
Purchase #6	$102.25	9.346%	$111.8063	$111.81	$111.80	$111.80
Purchase #7	$61.38	10.518%	$67.8359	$67.84	$67.85	$67.80
7 purchase totals =	$1,079.59		$1,151.3062	$1,151.31	$1,151.30	$1,151.20