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	$36.43	4.857%	$38.1994	$38.20	$38.20	$38.20
Purchase #2	$72.34	7.728%	$77.9304	$77.93	$77.95	$77.90
Purchase #3	$37.32	4.260%	$38.9098	$38.91	$38.90	$38.90
Purchase #4	$161.27	11.738%	$180.1999	$180.20	$180.20	$180.20
Purchase #5	$148.68	12.126%	$166.7089	$166.71	$166.70	$166.70
Purchase #6	$126.25	6.149%	$134.0131	$134.01	$134.00	$134.00
Purchase #7	$40.54	12.155%	$45.4676	$45.47	$45.45	$45.50
7 purchase totals =	$622.83		$681.4291	$681.43	$681.40	$681.40