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	$120.42	5.363%	$126.8781	$126.88	$126.90	$126.90
Purchase #2	$127.58	3.339%	$131.8399	$131.84	$131.85	$131.80
Purchase #3	$91.87	4.503%	$96.0069	$96.01	$96.00	$96.00
Purchase #4	$47.85	10.745%	$52.9915	$52.99	$53.00	$53.00
Purchase #5	$52.64	9.268%	$57.5187	$57.52	$57.50	$57.50
Purchase #6	$40.27	13.404%	$45.6678	$45.67	$45.65	$45.70
Purchase #7	$41.55	3.315%	$42.9274	$42.93	$42.95	$42.90
7 purchase totals =	$522.18		$553.8303	$553.84	$553.85	$553.80