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	$175.43	3.415%	$181.4209	$181.42	$181.40	$181.40
Purchase #2	$96.58	9.225%	$105.4895	$105.49	$105.50	$105.50
Purchase #3	$22.83	11.653%	$25.4904	$25.49	$25.50	$25.50
Purchase #4	$130.69	6.656%	$139.3887	$139.39	$139.40	$139.40
Purchase #5	$147.52	8.836%	$160.5549	$160.55	$160.55	$160.60
Purchase #6	$49.41	6.451%	$52.5974	$52.60	$52.60	$52.60
Purchase #7	$48.29	4.854%	$50.634	$50.63	$50.65	$50.60
7 purchase totals =	$670.75		$715.5758	$715.57	$715.60	$715.60