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	$78.76	6.367%	$83.7746	$83.77	$83.75	$83.80
Purchase #2	$241.41	11.634%	$269.4956	$269.50	$269.50	$269.50
Purchase #3	$220.40	13.223%	$249.5435	$249.54	$249.55	$249.50
Purchase #4	$148.75	7.433%	$159.8066	$159.81	$159.80	$159.80
Purchase #5	$59.31	13.371%	$67.2403	$67.24	$67.25	$67.20
Purchase #6	$82.27	10.143%	$90.6146	$90.61	$90.60	$90.60
Purchase #7	$249.53	5.451%	$263.1319	$263.13	$263.15	$263.10
7 purchase totals =	$1,080.43		$1,183.6071	$1,183.60	$1,183.60	$1,183.50