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	$91.81	9.551%	$100.5788	$100.58	$100.60	$100.60
Purchase #2	$50.26	9.785%	$55.1779	$55.18	$55.20	$55.20
Purchase #3	$78.72	9.640%	$86.3086	$86.31	$86.30	$86.30
Purchase #4	$26.59	10.622%	$29.4144	$29.41	$29.40	$29.40
Purchase #5	$27.68	4.519%	$28.9309	$28.93	$28.95	$28.90
Purchase #6	$78.29	10.760%	$86.714	$86.71	$86.70	$86.70
Purchase #7	$90.69	4.294%	$94.5842	$94.58	$94.60	$94.60
7 purchase totals =	$444.04		$481.7088	$481.70	$481.75	$481.70