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	$111.26	11.293%	$123.8246	$123.82	$123.80	$123.80
Purchase #2	$110.62	10.774%	$122.5382	$122.54	$122.55	$122.50
Purchase #3	$166.33	11.117%	$184.8209	$184.82	$184.80	$184.80
Purchase #4	$64.72	4.627%	$67.7146	$67.71	$67.70	$67.70
Purchase #5	$68.26	6.356%	$72.5986	$72.60	$72.60	$72.60
Purchase #6	$56.47	13.213%	$63.9314	$63.93	$63.95	$63.90
Purchase #7	$55.84	13.418%	$63.3326	$63.33	$63.35	$63.30
7 purchase totals =	$633.50		$698.7609	$698.75	$698.75	$698.60