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	$151.47	12.739%	$170.7658	$170.77	$170.75	$170.80
Purchase #2	$68.52	3.783%	$71.1121	$71.11	$71.10	$71.10
Purchase #3	$59.30	13.712%	$67.4312	$67.43	$67.45	$67.40
Purchase #4	$225.91	12.240%	$253.5614	$253.56	$253.55	$253.60
Purchase #5	$174.86	5.792%	$184.9879	$184.99	$185.00	$185.00
Purchase #6	$7.52	5.420%	$7.9276	$7.93	$7.95	$7.90
Purchase #7	$35.88	13.740%	$40.8099	$40.81	$40.80	$40.80
7 purchase totals =	$723.46		$796.5959	$796.60	$796.60	$796.60