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	$12.75	4.241%	$13.2907	$13.29	$13.30	$13.30
Purchase #2	$49.35	10.804%	$54.6818	$54.68	$54.70	$54.70
Purchase #3	$8.81	5.437%	$9.289	$9.29	$9.30	$9.30
Purchase #4	$243.43	5.139%	$255.9399	$255.94	$255.95	$255.90
Purchase #5	$154.59	11.555%	$172.4529	$172.45	$172.45	$172.50
Purchase #6	$132.56	7.793%	$142.8904	$142.89	$142.90	$142.90
Purchase #7	$39.47	8.702%	$42.9047	$42.90	$42.90	$42.90
7 purchase totals =	$640.96		$691.4494	$691.44	$691.50	$691.50