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	$96.87	3.688%	$100.4426	$100.44	$100.45	$100.40
Purchase #2	$142.82	10.744%	$158.1646	$158.16	$158.15	$158.20
Purchase #3	$62.34	13.873%	$70.9884	$70.99	$71.00	$71.00
Purchase #4	$172.80	4.771%	$181.0443	$181.04	$181.05	$181.00
Purchase #5	$222.67	11.745%	$248.8226	$248.82	$248.80	$248.80
Purchase #6	$56.89	13.517%	$64.5798	$64.58	$64.60	$64.60
Purchase #7	$190.65	13.743%	$216.851	$216.85	$216.85	$216.90
7 purchase totals =	$945.04		$1,040.8933	$1,040.88	$1,040.90	$1,040.90