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	$17.83	7.180%	$19.1102	$19.11	$19.10	$19.10
Purchase #2	$144.85	4.453%	$151.3002	$151.30	$151.30	$151.30
Purchase #3	$123.47	3.612%	$127.9297	$127.93	$127.95	$127.90
Purchase #4	$184.33	8.457%	$199.9188	$199.92	$199.90	$199.90
Purchase #5	$144.97	3.566%	$150.1396	$150.14	$150.15	$150.10
Purchase #6	$80.25	11.279%	$89.3014	$89.30	$89.30	$89.30
Purchase #7	$34.81	9.856%	$38.2409	$38.24	$38.25	$38.20
7 purchase totals =	$730.51		$775.9408	$775.94	$775.95	$775.80