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	$8.77	8.820%	$9.5435	$9.54	$9.55	$9.50
Purchase #2	$173.65	7.873%	$187.3215	$187.32	$187.30	$187.30
Purchase #3	$45.37	10.797%	$50.2686	$50.27	$50.25	$50.30
Purchase #4	$167.37	3.500%	$173.228	$173.23	$173.25	$173.20
Purchase #5	$102.32	7.637%	$110.1342	$110.13	$110.15	$110.10
Purchase #6	$161.86	6.285%	$172.0329	$172.03	$172.05	$172.00
Purchase #7	$86.49	3.187%	$89.2464	$89.25	$89.25	$89.20
7 purchase totals =	$745.83		$791.7751	$791.77	$791.80	$791.60