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	$68.26	6.196%	$72.4894	$72.49	$72.50	$72.50
Purchase #2	$246.72	11.689%	$275.5591	$275.56	$275.55	$275.60
Purchase #3	$195.79	3.248%	$202.1493	$202.15	$202.15	$202.10
Purchase #4	$34.75	6.184%	$36.8989	$36.90	$36.90	$36.90
Purchase #5	$144.62	9.384%	$158.1911	$158.19	$158.20	$158.20
Purchase #6	$158.67	8.159%	$171.6159	$171.62	$171.60	$171.60
Purchase #7	$155.51	11.600%	$173.5492	$173.55	$173.55	$173.50
7 purchase totals =	$1,004.32		$1,090.4529	$1,090.46	$1,090.45	$1,090.40