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	$160.83	6.261%	$170.8996	$170.90	$170.90	$170.90
Purchase #2	$185.55	5.821%	$196.3509	$196.35	$196.35	$196.40
Purchase #3	$153.60	13.687%	$174.6232	$174.62	$174.60	$174.60
Purchase #4	$35.60	13.213%	$40.3038	$40.30	$40.30	$40.30
Purchase #5	$181.67	4.720%	$190.2448	$190.24	$190.25	$190.20
Purchase #6	$156.71	10.506%	$173.174	$173.17	$173.15	$173.20
Purchase #7	$92.56	9.432%	$101.2903	$101.29	$101.30	$101.30
7 purchase totals =	$966.52		$1,046.8866	$1,046.87	$1,046.85	$1,046.90