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	$10.60	11.457%	$11.8144	$11.81	$11.80	$11.80
Purchase #2	$67.50	7.158%	$72.3317	$72.33	$72.35	$72.30
Purchase #3	$221.72	13.451%	$251.5436	$251.54	$251.55	$251.50
Purchase #4	$151.61	4.779%	$158.8554	$158.86	$158.85	$158.90
Purchase #5	$89.71	8.643%	$97.4636	$97.46	$97.45	$97.50
Purchase #6	$150.85	12.445%	$169.6233	$169.62	$169.60	$169.60
Purchase #7	$150.25	7.333%	$161.2678	$161.27	$161.25	$161.30
7 purchase totals =	$842.24		$922.8998	$922.89	$922.85	$922.90