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	$139.86	12.402%	$157.2054	$157.21	$157.20	$157.20
Purchase #2	$174.62	5.174%	$183.6548	$183.65	$183.65	$183.70
Purchase #3	$185.61	13.338%	$210.3667	$210.37	$210.35	$210.40
Purchase #4	$100.52	10.533%	$111.1078	$111.11	$111.10	$111.10
Purchase #5	$69.39	7.530%	$74.6151	$74.62	$74.60	$74.60
Purchase #6	$102.86	10.665%	$113.83	$113.83	$113.85	$113.80
Purchase #7	$176.89	13.265%	$200.3545	$200.35	$200.35	$200.40
7 purchase totals =	$949.75		$1,051.1343	$1,051.14	$1,051.10	$1,051.20