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	$125.56	11.314%	$139.7659	$139.77	$139.75	$139.80
Purchase #2	$76.88	6.865%	$82.1578	$82.16	$82.15	$82.20
Purchase #3	$74.92	6.277%	$79.6227	$79.62	$79.60	$79.60
Purchase #4	$74.42	5.113%	$78.2251	$78.23	$78.25	$78.20
Purchase #5	$47.57	11.810%	$53.188	$53.19	$53.20	$53.20
Purchase #6	$133.77	8.351%	$144.9411	$144.94	$144.95	$144.90
Purchase #7	$111.81	6.155%	$118.6919	$118.69	$118.70	$118.70
7 purchase totals =	$644.93		$696.5925	$696.60	$696.60	$696.60