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	$83.71	5.746%	$88.52	$88.52	$88.50	$88.50
Purchase #2	$89.25	7.765%	$96.1803	$96.18	$96.20	$96.20
Purchase #3	$20.37	6.258%	$21.6448	$21.64	$21.65	$21.60
Purchase #4	$90.54	10.286%	$99.8529	$99.85	$99.85	$99.90
Purchase #5	$210.75	13.567%	$239.3425	$239.34	$239.35	$239.30
Purchase #6	$76.73	4.828%	$80.4345	$80.43	$80.45	$80.40
Purchase #7	$111.44	6.406%	$118.5788	$118.58	$118.60	$118.60
7 purchase totals =	$682.79		$744.5538	$744.54	$744.60	$744.50