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	$144.86	6.539%	$154.3324	$154.33	$154.35	$154.30
Purchase #2	$32.65	9.564%	$35.7726	$35.77	$35.75	$35.80
Purchase #3	$98.55	6.445%	$104.9015	$104.90	$104.90	$104.90
Purchase #4	$59.85	6.748%	$63.8887	$63.89	$63.90	$63.90
Purchase #5	$147.47	8.857%	$160.5314	$160.53	$160.55	$160.50
Purchase #6	$134.39	12.633%	$151.3675	$151.37	$151.35	$151.40
Purchase #7	$136.83	13.861%	$155.796	$155.80	$155.80	$155.80
7 purchase totals =	$754.60		$826.5901	$826.59	$826.60	$826.60