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	$238.35	12.224%	$267.4859	$267.49	$267.50	$267.50
Purchase #2	$59.73	9.445%	$65.3715	$65.37	$65.35	$65.40
Purchase #3	$210.53	7.112%	$225.5029	$225.50	$225.50	$225.50
Purchase #4	$134.29	8.303%	$145.4401	$145.44	$145.45	$145.40
Purchase #5	$35.25	5.725%	$37.2681	$37.27	$37.25	$37.30
Purchase #6	$241.85	4.698%	$253.2121	$253.21	$253.20	$253.20
Purchase #7	$209.50	9.124%	$228.6148	$228.61	$228.60	$228.60
7 purchase totals =	$1,129.50		$1,222.8954	$1,222.89	$1,222.85	$1,222.90