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	$38.95	6.503%	$41.4829	$41.48	$41.50	$41.50
Purchase #2	$17.72	10.240%	$19.5345	$19.53	$19.55	$19.50
Purchase #3	$72.51	3.109%	$74.7643	$74.76	$74.75	$74.80
Purchase #4	$49.71	13.140%	$56.2419	$56.24	$56.25	$56.20
Purchase #5	$38.59	10.379%	$42.5953	$42.60	$42.60	$42.60
Purchase #6	$55.29	7.135%	$59.2349	$59.23	$59.25	$59.20
Purchase #7	$224.99	4.854%	$235.911	$235.91	$235.90	$235.90
7 purchase totals =	$497.76		$529.7648	$529.75	$529.80	$529.70