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	$50.64	8.793%	$55.0928	$55.09	$55.10	$55.10
Purchase #2	$220.69	11.599%	$246.2878	$246.29	$246.30	$246.30
Purchase #3	$105.72	5.395%	$111.4236	$111.42	$111.40	$111.40
Purchase #4	$212.46	12.182%	$238.3419	$238.34	$238.35	$238.30
Purchase #5	$170.32	6.142%	$180.7811	$180.78	$180.80	$180.80
Purchase #6	$79.58	10.695%	$88.0911	$88.09	$88.10	$88.10
Purchase #7	$145.95	5.404%	$153.8371	$153.84	$153.85	$153.80
7 purchase totals =	$985.36		$1,073.8554	$1,073.85	$1,073.90	$1,073.80