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	$20.60	5.498%	$21.7326	$21.73	$21.75	$21.70
Purchase #2	$219.35	4.641%	$229.53	$229.53	$229.55	$229.50
Purchase #3	$52.81	4.428%	$55.1484	$55.15	$55.15	$55.10
Purchase #4	$140.92	5.559%	$148.7537	$148.75	$148.75	$148.80
Purchase #5	$217.85	6.226%	$231.4133	$231.41	$231.40	$231.40
Purchase #6	$243.51	3.326%	$251.6091	$251.61	$251.60	$251.60
Purchase #7	$130.86	10.656%	$144.8044	$144.80	$144.80	$144.80
7 purchase totals =	$1,025.90		$1,082.9915	$1,082.98	$1,083.00	$1,082.90