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	$123.79	13.687%	$140.7331	$140.73	$140.75	$140.70
Purchase #2	$137.60	6.728%	$146.8577	$146.86	$146.85	$146.90
Purchase #3	$92.49	8.367%	$100.2286	$100.23	$100.25	$100.20
Purchase #4	$14.48	5.579%	$15.2878	$15.29	$15.30	$15.30
Purchase #5	$188.64	5.109%	$198.2776	$198.28	$198.30	$198.30
Purchase #6	$228.65	9.435%	$250.2231	$250.22	$250.20	$250.20
Purchase #7	$73.37	6.605%	$78.2161	$78.22	$78.20	$78.20
7 purchase totals =	$859.02		$929.8240	$929.83	$929.85	$929.80