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	$67.91	6.646%	$72.4233	$72.42	$72.40	$72.40
Purchase #2	$83.63	5.663%	$88.366	$88.37	$88.35	$88.40
Purchase #3	$175.45	5.228%	$184.6225	$184.62	$184.60	$184.60
Purchase #4	$183.29	5.218%	$192.8541	$192.85	$192.85	$192.90
Purchase #5	$164.82	11.631%	$183.9902	$183.99	$184.00	$184.00
Purchase #6	$86.88	3.773%	$90.158	$90.16	$90.15	$90.20
Purchase #7	$156.87	9.545%	$171.8432	$171.84	$171.85	$171.80
7 purchase totals =	$918.85		$984.2573	$984.25	$984.20	$984.30