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	$104.42	6.471%	$111.177	$111.18	$111.20	$111.20
Purchase #2	$89.65	12.251%	$100.633	$100.63	$100.65	$100.60
Purchase #3	$82.60	13.563%	$93.803	$93.80	$93.80	$93.80
Purchase #4	$64.39	4.850%	$67.5129	$67.51	$67.50	$67.50
Purchase #5	$95.65	8.514%	$103.7936	$103.79	$103.80	$103.80
Purchase #6	$5.36	11.186%	$5.9596	$5.96	$5.95	$6.00
Purchase #7	$113.44	3.376%	$117.2697	$117.27	$117.25	$117.30
7 purchase totals =	$555.51		$600.1488	$600.14	$600.15	$600.20