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	$107.69	6.620%	$114.8191	$114.82	$114.80	$114.80
Purchase #2	$159.68	9.490%	$174.8336	$174.83	$174.85	$174.80
Purchase #3	$40.54	12.400%	$45.567	$45.57	$45.55	$45.60
Purchase #4	$79.50	9.780%	$87.2751	$87.28	$87.30	$87.30
Purchase #5	$244.62	4.479%	$255.5765	$255.58	$255.60	$255.60
Purchase #6	$54.40	12.267%	$61.0732	$61.07	$61.05	$61.10
Purchase #7	$183.65	3.166%	$189.4644	$189.46	$189.45	$189.50
7 purchase totals =	$870.08		$928.6089	$928.61	$928.60	$928.70