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	$43.54	4.514%	$45.5054	$45.51	$45.50	$45.50
Purchase #2	$222.46	3.116%	$229.3919	$229.39	$229.40	$229.40
Purchase #3	$131.40	8.818%	$142.9869	$142.99	$143.00	$143.00
Purchase #4	$174.27	8.668%	$189.3757	$189.38	$189.40	$189.40
Purchase #5	$135.75	6.583%	$144.6864	$144.69	$144.70	$144.70
Purchase #6	$157.63	10.716%	$174.5216	$174.52	$174.50	$174.50
Purchase #7	$161.98	6.544%	$172.58	$172.58	$172.60	$172.60
7 purchase totals =	$1,027.03		$1,099.0479	$1,099.06	$1,099.10	$1,099.10