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	$134.42	5.755%	$142.1559	$142.16	$142.15	$142.20
Purchase #2	$149.81	10.326%	$165.2794	$165.28	$165.30	$165.30
Purchase #3	$117.26	11.628%	$130.895	$130.90	$130.90	$130.90
Purchase #4	$136.61	11.633%	$152.5018	$152.50	$152.50	$152.50
Purchase #5	$90.43	4.586%	$94.5771	$94.58	$94.60	$94.60
Purchase #6	$143.26	4.863%	$150.2267	$150.23	$150.25	$150.20
Purchase #7	$132.91	7.619%	$143.0364	$143.04	$143.05	$143.00
7 purchase totals =	$904.70		$978.6723	$978.69	$978.75	$978.70