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	$29.36	6.349%	$31.2241	$31.22	$31.20	$31.20
Purchase #2	$44.32	3.342%	$45.8012	$45.80	$45.80	$45.80
Purchase #3	$158.36	7.505%	$170.2449	$170.24	$170.25	$170.20
Purchase #4	$214.48	6.492%	$228.404	$228.40	$228.40	$228.40
Purchase #5	$185.69	10.213%	$204.6545	$204.65	$204.65	$204.70
Purchase #6	$166.42	5.285%	$175.2153	$175.22	$175.20	$175.20
Purchase #7	$223.91	9.593%	$245.3897	$245.39	$245.40	$245.40
7 purchase totals =	$1,022.54		$1,100.9337	$1,100.92	$1,100.90	$1,100.90