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	$38.98	4.283%	$40.6495	$40.65	$40.65	$40.60
Purchase #2	$197.85	6.502%	$210.7142	$210.71	$210.70	$210.70
Purchase #3	$80.81	5.764%	$85.4679	$85.47	$85.45	$85.50
Purchase #4	$98.76	10.295%	$108.9273	$108.93	$108.95	$108.90
Purchase #5	$22.86	9.113%	$24.9432	$24.94	$24.95	$24.90
Purchase #6	$52.52	12.743%	$59.2126	$59.21	$59.20	$59.20
Purchase #7	$120.89	11.135%	$134.3511	$134.35	$134.35	$134.40
7 purchase totals =	$612.67		$664.2658	$664.26	$664.25	$664.20