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	$172.41	3.394%	$178.2616	$178.26	$178.25	$178.30
Purchase #2	$102.65	8.416%	$111.289	$111.29	$111.30	$111.30
Purchase #3	$6.59	6.267%	$7.003	$7.00	$7.00	$7.00
Purchase #4	$27.87	11.848%	$31.172	$31.17	$31.15	$31.20
Purchase #5	$169.79	5.184%	$178.5919	$178.59	$178.60	$178.60
Purchase #6	$181.99	12.171%	$204.14	$204.14	$204.15	$204.10
Purchase #7	$230.70	8.481%	$250.2657	$250.27	$250.25	$250.30
7 purchase totals =	$892.00		$960.7232	$960.72	$960.70	$960.80