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	$71.34	12.833%	$80.4951	$80.50	$80.50	$80.50
Purchase #2	$67.60	4.660%	$70.7502	$70.75	$70.75	$70.80
Purchase #3	$50.99	6.300%	$54.2024	$54.20	$54.20	$54.20
Purchase #4	$66.39	5.667%	$70.1523	$70.15	$70.15	$70.20
Purchase #5	$216.66	3.204%	$223.6018	$223.60	$223.60	$223.60
Purchase #6	$230.61	8.222%	$249.5708	$249.57	$249.55	$249.60
Purchase #7	$208.66	10.179%	$229.8995	$229.90	$229.90	$229.90
7 purchase totals =	$912.25		$978.6721	$978.67	$978.65	$978.80