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	$11.44	11.120%	$12.7121	$12.71	$12.70	$12.70
Purchase #2	$179.39	5.657%	$189.5381	$189.54	$189.55	$189.50
Purchase #3	$241.90	9.328%	$264.4644	$264.46	$264.45	$264.50
Purchase #4	$223.51	5.468%	$235.7315	$235.73	$235.75	$235.70
Purchase #5	$160.99	3.338%	$166.3638	$166.36	$166.35	$166.40
Purchase #6	$169.87	10.566%	$187.8185	$187.82	$187.80	$187.80
Purchase #7	$97.63	13.846%	$111.1478	$111.15	$111.15	$111.10
7 purchase totals =	$1,084.73		$1,167.7762	$1,167.77	$1,167.75	$1,167.70