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	$15.48	6.120%	$16.4274	$16.43	$16.45	$16.40
Purchase #2	$144.27	7.354%	$154.8796	$154.88	$154.90	$154.90
Purchase #3	$137.56	6.261%	$146.1726	$146.17	$146.15	$146.20
Purchase #4	$91.30	9.243%	$99.7389	$99.74	$99.75	$99.70
Purchase #5	$189.77	3.734%	$196.856	$196.86	$196.85	$196.90
Purchase #6	$207.47	3.334%	$214.387	$214.39	$214.40	$214.40
Purchase #7	$129.39	11.749%	$144.592	$144.59	$144.60	$144.60
7 purchase totals =	$915.24		$973.0535	$973.06	$973.10	$973.10