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	$24.72	13.222%	$27.9885	$27.99	$28.00	$28.00
Purchase #2	$141.77	6.387%	$150.8248	$150.82	$150.80	$150.80
Purchase #3	$250.26	5.759%	$264.6725	$264.67	$264.65	$264.70
Purchase #4	$150.70	5.229%	$158.5801	$158.58	$158.60	$158.60
Purchase #5	$144.80	10.264%	$159.6623	$159.66	$159.65	$159.70
Purchase #6	$145.61	5.781%	$154.0277	$154.03	$154.05	$154.00
Purchase #7	$239.90	6.470%	$255.4215	$255.42	$255.40	$255.40
7 purchase totals =	$1,097.76		$1,171.1774	$1,171.17	$1,171.15	$1,171.20