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	$16.33	9.192%	$17.8311	$17.83	$17.85	$17.80
Purchase #2	$99.82	8.328%	$108.133	$108.13	$108.15	$108.10
Purchase #3	$78.87	5.182%	$82.957	$82.96	$82.95	$83.00
Purchase #4	$108.78	11.338%	$121.1135	$121.11	$121.10	$121.10
Purchase #5	$101.51	5.597%	$107.1915	$107.19	$107.20	$107.20
Purchase #6	$98.52	11.513%	$109.8626	$109.86	$109.85	$109.90
Purchase #7	$178.83	3.485%	$185.0622	$185.06	$185.05	$185.10
7 purchase totals =	$682.66		$732.1509	$732.14	$732.15	$732.20