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	$148.92	6.329%	$158.3451	$158.35	$158.35	$158.30
Purchase #2	$111.29	13.427%	$126.2329	$126.23	$126.25	$126.20
Purchase #3	$82.57	3.135%	$85.1586	$85.16	$85.15	$85.20
Purchase #4	$37.79	13.286%	$42.8108	$42.81	$42.80	$42.80
Purchase #5	$93.44	7.342%	$100.3004	$100.30	$100.30	$100.30
Purchase #6	$33.36	7.105%	$35.7302	$35.73	$35.75	$35.70
Purchase #7	$68.98	4.389%	$72.0075	$72.01	$72.00	$72.00
7 purchase totals =	$576.35		$620.5855	$620.59	$620.60	$620.50