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	$21.44	4.287%	$22.3591	$22.36	$22.35	$22.40
Purchase #2	$190.86	11.552%	$212.9081	$212.91	$212.90	$212.90
Purchase #3	$53.26	6.696%	$56.8263	$56.83	$56.85	$56.80
Purchase #4	$207.39	8.748%	$225.5325	$225.53	$225.55	$225.50
Purchase #5	$29.98	9.816%	$32.9228	$32.92	$32.90	$32.90
Purchase #6	$18.63	3.405%	$19.2644	$19.26	$19.25	$19.30
Purchase #7	$90.69	10.412%	$100.1326	$100.13	$100.15	$100.10
7 purchase totals =	$612.25		$669.9458	$669.94	$669.95	$669.90