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	$36.77	4.717%	$38.5044	$38.50	$38.50	$38.50
Purchase #2	$34.75	6.753%	$37.0967	$37.10	$37.10	$37.10
Purchase #3	$173.33	10.274%	$191.1379	$191.14	$191.15	$191.10
Purchase #4	$116.61	9.137%	$127.2647	$127.26	$127.25	$127.30
Purchase #5	$66.88	4.367%	$69.8006	$69.80	$69.80	$69.80
Purchase #6	$186.91	10.460%	$206.4608	$206.46	$206.45	$206.50
Purchase #7	$109.39	4.521%	$114.3355	$114.34	$114.35	$114.30
7 purchase totals =	$724.64		$784.6006	$784.60	$784.60	$784.60