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	$152.41	8.321%	$165.092	$165.09	$165.10	$165.10
Purchase #2	$225.35	8.548%	$244.6129	$244.61	$244.60	$244.60
Purchase #3	$103.86	10.465%	$114.7289	$114.73	$114.75	$114.70
Purchase #4	$150.72	11.496%	$168.0468	$168.05	$168.05	$168.00
Purchase #5	$29.72	10.406%	$32.8127	$32.81	$32.80	$32.80
Purchase #6	$217.53	12.736%	$245.2346	$245.23	$245.25	$245.20
Purchase #7	$145.88	3.723%	$151.3111	$151.31	$151.30	$151.30
7 purchase totals =	$1,025.47		$1,121.8390	$1,121.83	$1,121.85	$1,121.70