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	$123.72	12.582%	$139.2865	$139.29	$139.30	$139.30
Purchase #2	$91.49	8.406%	$99.1806	$99.18	$99.20	$99.20
Purchase #3	$192.72	10.273%	$212.5181	$212.52	$212.50	$212.50
Purchase #4	$161.66	6.640%	$172.3942	$172.39	$172.40	$172.40
Purchase #5	$158.35	3.707%	$164.22	$164.22	$164.20	$164.20
Purchase #6	$55.93	11.114%	$62.1461	$62.15	$62.15	$62.10
Purchase #7	$118.98	8.736%	$129.3741	$129.37	$129.35	$129.40
7 purchase totals =	$902.85		$979.1196	$979.12	$979.10	$979.10