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	$18.46	10.335%	$20.3678	$20.37	$20.35	$20.40
Purchase #2	$240.42	5.591%	$253.8619	$253.86	$253.85	$253.90
Purchase #3	$125.31	13.764%	$142.5577	$142.56	$142.55	$142.60
Purchase #4	$230.82	9.364%	$252.434	$252.43	$252.45	$252.40
Purchase #5	$191.75	13.432%	$217.5059	$217.51	$217.50	$217.50
Purchase #6	$77.49	5.143%	$81.4753	$81.48	$81.50	$81.50
Purchase #7	$163.62	11.526%	$182.4788	$182.48	$182.50	$182.50
7 purchase totals =	$1,047.87		$1,150.6814	$1,150.69	$1,150.70	$1,150.80