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	$128.78	13.745%	$146.4808	$146.48	$146.50	$146.50
Purchase #2	$19.42	3.721%	$20.1426	$20.14	$20.15	$20.10
Purchase #3	$27.49	5.194%	$28.9178	$28.92	$28.90	$28.90
Purchase #4	$167.40	9.479%	$183.2678	$183.27	$183.25	$183.30
Purchase #5	$139.47	11.395%	$155.3626	$155.36	$155.35	$155.40
Purchase #6	$62.56	3.219%	$64.5738	$64.57	$64.55	$64.60
Purchase #7	$101.89	10.337%	$112.4224	$112.42	$112.40	$112.40
7 purchase totals =	$647.01		$711.1678	$711.16	$711.10	$711.20