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	$40.73	3.624%	$42.2061	$42.21	$42.20	$42.20
Purchase #2	$137.71	13.271%	$155.9855	$155.99	$156.00	$156.00
Purchase #3	$180.99	8.629%	$196.6076	$196.61	$196.60	$196.60
Purchase #4	$212.69	8.273%	$230.2858	$230.29	$230.30	$230.30
Purchase #5	$177.30	4.795%	$185.8015	$185.80	$185.80	$185.80
Purchase #6	$176.43	6.315%	$187.5716	$187.57	$187.55	$187.60
Purchase #7	$63.45	13.705%	$72.1458	$72.15	$72.15	$72.10
7 purchase totals =	$989.30		$1,070.6039	$1,070.62	$1,070.60	$1,070.60