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	$19.38	10.250%	$21.3665	$21.37	$21.35	$21.40
Purchase #2	$52.99	11.692%	$59.1856	$59.19	$59.20	$59.20
Purchase #3	$172.79	13.589%	$196.2704	$196.27	$196.25	$196.30
Purchase #4	$190.35	8.636%	$206.7886	$206.79	$206.80	$206.80
Purchase #5	$191.60	4.657%	$200.5228	$200.52	$200.50	$200.50
Purchase #6	$45.72	3.704%	$47.4135	$47.41	$47.40	$47.40
Purchase #7	$52.82	11.563%	$58.9276	$58.93	$58.95	$58.90
7 purchase totals =	$725.65		$790.4750	$790.48	$790.45	$790.50