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	$19.53	8.575%	$21.2047	$21.20	$21.20	$21.20
Purchase #2	$134.96	11.537%	$150.5303	$150.53	$150.55	$150.50
Purchase #3	$172.28	10.224%	$189.8939	$189.89	$189.90	$189.90
Purchase #4	$48.51	12.124%	$54.3914	$54.39	$54.40	$54.40
Purchase #5	$63.80	7.847%	$68.8064	$68.81	$68.80	$68.80
Purchase #6	$51.81	11.488%	$57.7619	$57.76	$57.75	$57.80
Purchase #7	$17.36	8.401%	$18.8184	$18.82	$18.80	$18.80
7 purchase totals =	$508.25		$561.4070	$561.40	$561.40	$561.40