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	$153.28	8.458%	$166.2444	$166.24	$166.25	$166.20
Purchase #2	$158.39	4.459%	$165.4526	$165.45	$165.45	$165.50
Purchase #3	$93.70	7.373%	$100.6085	$100.61	$100.60	$100.60
Purchase #4	$246.89	10.698%	$273.3023	$273.30	$273.30	$273.30
Purchase #5	$227.98	4.447%	$238.1183	$238.12	$238.10	$238.10
Purchase #6	$134.67	13.282%	$152.5569	$152.56	$152.55	$152.60
Purchase #7	$227.62	6.316%	$241.9965	$242.00	$242.00	$242.00
7 purchase totals =	$1,242.53		$1,338.2795	$1,338.28	$1,338.25	$1,338.30