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	$16.72	6.641%	$17.8304	$17.83	$17.85	$17.80
Purchase #2	$69.77	7.256%	$74.8325	$74.83	$74.85	$74.80
Purchase #3	$227.43	7.793%	$245.1536	$245.15	$245.15	$245.20
Purchase #4	$120.97	10.873%	$134.1231	$134.12	$134.10	$134.10
Purchase #5	$102.49	9.779%	$112.5125	$112.51	$112.50	$112.50
Purchase #6	$123.42	3.313%	$127.5089	$127.51	$127.50	$127.50
Purchase #7	$137.35	3.621%	$142.3234	$142.32	$142.30	$142.30
7 purchase totals =	$798.15		$854.2844	$854.27	$854.25	$854.20