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	$183.57	11.591%	$204.8476	$204.85	$204.85	$204.80
Purchase #2	$95.82	3.828%	$99.488	$99.49	$99.50	$99.50
Purchase #3	$96.47	3.849%	$100.1831	$100.18	$100.20	$100.20
Purchase #4	$65.54	6.251%	$69.6369	$69.64	$69.65	$69.60
Purchase #5	$41.87	7.520%	$45.0186	$45.02	$45.00	$45.00
Purchase #6	$50.98	8.261%	$55.1915	$55.19	$55.20	$55.20
Purchase #7	$54.60	4.388%	$56.9958	$57.00	$57.00	$57.00
7 purchase totals =	$588.85		$631.3615	$631.37	$631.40	$631.30