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	$133.59	8.378%	$144.7822	$144.78	$144.80	$144.80
Purchase #2	$75.40	4.119%	$78.5057	$78.51	$78.50	$78.50
Purchase #3	$146.56	7.725%	$157.8818	$157.88	$157.90	$157.90
Purchase #4	$174.87	6.203%	$185.7172	$185.72	$185.70	$185.70
Purchase #5	$63.86	12.383%	$71.7678	$71.77	$71.75	$71.80
Purchase #6	$143.58	12.658%	$161.7544	$161.75	$161.75	$161.80
Purchase #7	$54.38	12.162%	$60.9937	$60.99	$61.00	$61.00
7 purchase totals =	$792.24		$861.4028	$861.40	$861.40	$861.50