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	$139.88	9.730%	$153.4903	$153.49	$153.50	$153.50
Purchase #2	$232.87	3.262%	$240.4662	$240.47	$240.45	$240.50
Purchase #3	$30.55	6.813%	$32.6314	$32.63	$32.65	$32.60
Purchase #4	$67.32	10.611%	$74.4633	$74.46	$74.45	$74.50
Purchase #5	$99.59	13.840%	$113.3733	$113.37	$113.35	$113.40
Purchase #6	$180.88	8.229%	$195.7646	$195.76	$195.75	$195.80
Purchase #7	$78.94	13.502%	$89.5985	$89.60	$89.60	$89.60
7 purchase totals =	$830.03		$899.7876	$899.78	$899.75	$899.90