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	$25.64	11.456%	$28.5773	$28.58	$28.60	$28.60
Purchase #2	$74.39	5.835%	$78.7307	$78.73	$78.75	$78.70
Purchase #3	$161.39	9.414%	$176.5833	$176.58	$176.60	$176.60
Purchase #4	$89.62	3.165%	$92.4565	$92.46	$92.45	$92.50
Purchase #5	$74.43	5.163%	$78.2728	$78.27	$78.25	$78.30
Purchase #6	$213.49	12.785%	$240.7847	$240.78	$240.80	$240.80
Purchase #7	$99.73	12.213%	$111.91	$111.91	$111.90	$111.90
7 purchase totals =	$738.69		$807.3153	$807.31	$807.35	$807.40