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	$107.43	11.760%	$120.0638	$120.06	$120.05	$120.10
Purchase #2	$214.29	13.138%	$242.4434	$242.44	$242.45	$242.40
Purchase #3	$95.71	5.173%	$100.6611	$100.66	$100.65	$100.70
Purchase #4	$67.69	8.383%	$73.3645	$73.36	$73.35	$73.40
Purchase #5	$118.63	9.786%	$130.2391	$130.24	$130.25	$130.20
Purchase #6	$40.71	13.145%	$46.0613	$46.06	$46.05	$46.10
Purchase #7	$84.39	6.141%	$89.5724	$89.57	$89.55	$89.60
7 purchase totals =	$728.85		$802.4056	$802.39	$802.35	$802.50