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	$138.28	5.645%	$146.0859	$146.09	$146.10	$146.10
Purchase #2	$58.31	5.105%	$61.2867	$61.29	$61.30	$61.30
Purchase #3	$138.61	3.499%	$143.46	$143.46	$143.45	$143.50
Purchase #4	$189.92	3.571%	$196.702	$196.70	$196.70	$196.70
Purchase #5	$116.35	11.829%	$130.113	$130.11	$130.10	$130.10
Purchase #6	$54.94	4.268%	$57.2848	$57.28	$57.30	$57.30
Purchase #7	$111.26	10.400%	$122.831	$122.83	$122.85	$122.80
7 purchase totals =	$807.67		$857.7634	$857.76	$857.80	$857.80