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	$176.79	6.358%	$188.0303	$188.03	$188.05	$188.00
Purchase #2	$158.88	8.798%	$172.8583	$172.86	$172.85	$172.90
Purchase #3	$63.45	12.804%	$71.5741	$71.57	$71.55	$71.60
Purchase #4	$128.93	12.823%	$145.4627	$145.46	$145.45	$145.50
Purchase #5	$83.26	10.430%	$91.944	$91.94	$91.95	$91.90
Purchase #6	$175.94	9.631%	$192.8848	$192.88	$192.90	$192.90
Purchase #7	$139.27	3.560%	$144.228	$144.23	$144.25	$144.20
7 purchase totals =	$926.52		$1,006.9822	$1,006.97	$1,007.00	$1,007.00