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	$236.91	8.102%	$256.1044	$256.10	$256.10	$256.10
Purchase #2	$127.96	13.757%	$145.5635	$145.56	$145.55	$145.60
Purchase #3	$230.49	11.565%	$257.1462	$257.15	$257.15	$257.10
Purchase #4	$230.74	4.238%	$240.5188	$240.52	$240.50	$240.50
Purchase #5	$86.31	4.687%	$90.3553	$90.36	$90.35	$90.40
Purchase #6	$34.85	6.798%	$37.2191	$37.22	$37.20	$37.20
Purchase #7	$86.38	13.271%	$97.8435	$97.84	$97.85	$97.80
7 purchase totals =	$1,033.64		$1,124.7508	$1,124.75	$1,124.70	$1,124.70