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	$87.71	3.235%	$90.5474	$90.55	$90.55	$90.50
Purchase #2	$166.37	13.311%	$188.5155	$188.52	$188.50	$188.50
Purchase #3	$81.72	12.330%	$91.7961	$91.80	$91.80	$91.80
Purchase #4	$48.67	12.195%	$54.6053	$54.61	$54.60	$54.60
Purchase #5	$66.67	7.185%	$71.4602	$71.46	$71.45	$71.50
Purchase #6	$201.32	7.704%	$216.8297	$216.83	$216.85	$216.80
Purchase #7	$78.75	12.793%	$88.8245	$88.82	$88.80	$88.80
7 purchase totals =	$731.21		$802.5787	$802.59	$802.55	$802.50