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	$113.91	13.452%	$129.2332	$129.23	$129.25	$129.20
Purchase #2	$217.76	12.749%	$245.5222	$245.52	$245.50	$245.50
Purchase #3	$23.36	5.190%	$24.5724	$24.57	$24.55	$24.60
Purchase #4	$80.65	11.397%	$89.8417	$89.84	$89.85	$89.80
Purchase #5	$100.92	10.142%	$111.1553	$111.16	$111.15	$111.20
Purchase #6	$96.65	5.675%	$102.1349	$102.13	$102.15	$102.10
Purchase #7	$139.34	3.791%	$144.6224	$144.62	$144.60	$144.60
7 purchase totals =	$772.59		$847.0821	$847.07	$847.05	$847.00