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	$115.83	7.161%	$124.1246	$124.12	$124.10	$124.10
Purchase #2	$142.47	8.627%	$154.7609	$154.76	$154.75	$154.80
Purchase #3	$106.89	12.205%	$119.9359	$119.94	$119.95	$119.90
Purchase #4	$17.33	6.629%	$18.4788	$18.48	$18.50	$18.50
Purchase #5	$150.60	5.196%	$158.4252	$158.43	$158.45	$158.40
Purchase #6	$199.92	11.825%	$223.5605	$223.56	$223.55	$223.60
Purchase #7	$124.35	5.245%	$130.8722	$130.87	$130.85	$130.90
7 purchase totals =	$857.39		$930.1581	$930.16	$930.15	$930.20