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	$80.99	10.305%	$89.336	$89.34	$89.35	$89.30
Purchase #2	$244.78	3.152%	$252.4955	$252.50	$252.50	$252.50
Purchase #3	$91.38	13.830%	$104.0179	$104.02	$104.00	$104.00
Purchase #4	$77.97	4.227%	$81.2658	$81.27	$81.25	$81.30
Purchase #5	$209.71	4.314%	$218.7569	$218.76	$218.75	$218.80
Purchase #6	$136.54	13.627%	$155.1463	$155.15	$155.15	$155.10
Purchase #7	$139.92	3.194%	$144.389	$144.39	$144.40	$144.40
7 purchase totals =	$981.29		$1,045.4074	$1,045.43	$1,045.40	$1,045.40