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	$244.61	6.228%	$259.8443	$259.84	$259.85	$259.80
Purchase #2	$95.37	13.689%	$108.4252	$108.43	$108.45	$108.40
Purchase #3	$103.57	8.757%	$112.6396	$112.64	$112.65	$112.60
Purchase #4	$226.35	6.405%	$240.8477	$240.85	$240.85	$240.80
Purchase #5	$16.50	13.790%	$18.7754	$18.78	$18.80	$18.80
Purchase #6	$146.30	3.470%	$151.3766	$151.38	$151.40	$151.40
Purchase #7	$233.28	10.696%	$258.2316	$258.23	$258.25	$258.20
7 purchase totals =	$1,065.98		$1,150.1404	$1,150.15	$1,150.25	$1,150.00