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	$170.33	4.696%	$178.3287	$178.33	$178.35	$178.30
Purchase #2	$72.55	7.700%	$78.1364	$78.14	$78.15	$78.10
Purchase #3	$56.52	6.773%	$60.3481	$60.35	$60.35	$60.30
Purchase #4	$11.54	3.859%	$11.9853	$11.99	$12.00	$12.00
Purchase #5	$161.62	6.534%	$172.1803	$172.18	$172.20	$172.20
Purchase #6	$132.55	6.255%	$140.841	$140.84	$140.85	$140.80
Purchase #7	$138.34	4.398%	$144.4242	$144.42	$144.40	$144.40
7 purchase totals =	$743.45		$786.2440	$786.25	$786.30	$786.10