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	$12.36	11.519%	$13.7837	$13.78	$13.80	$13.80
Purchase #2	$181.39	4.793%	$190.084	$190.08	$190.10	$190.10
Purchase #3	$50.52	6.730%	$53.92	$53.92	$53.90	$53.90
Purchase #4	$144.30	4.294%	$150.4962	$150.50	$150.50	$150.50
Purchase #5	$45.92	5.150%	$48.2849	$48.28	$48.30	$48.30
Purchase #6	$133.89	9.421%	$146.5038	$146.50	$146.50	$146.50
Purchase #7	$22.27	11.194%	$24.7629	$24.76	$24.75	$24.80
7 purchase totals =	$590.65		$627.8355	$627.82	$627.85	$627.90