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	$6.32	13.610%	$7.1802	$7.18	$7.20	$7.20
Purchase #2	$159.82	6.469%	$170.1588	$170.16	$170.15	$170.20
Purchase #3	$192.72	9.797%	$211.6008	$211.60	$211.60	$211.60
Purchase #4	$57.87	11.208%	$64.3561	$64.36	$64.35	$64.40
Purchase #5	$77.72	4.159%	$80.9524	$80.95	$80.95	$81.00
Purchase #6	$228.79	5.119%	$240.5018	$240.50	$240.50	$240.50
Purchase #7	$151.94	13.450%	$172.3759	$172.38	$172.40	$172.40
7 purchase totals =	$875.18		$947.1260	$947.13	$947.15	$947.30