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	$106.33	3.332%	$109.8729	$109.87	$109.85	$109.90
Purchase #2	$44.44	3.768%	$46.1145	$46.11	$46.10	$46.10
Purchase #3	$142.26	10.683%	$157.4576	$157.46	$157.45	$157.50
Purchase #4	$54.40	8.834%	$59.2057	$59.21	$59.20	$59.20
Purchase #5	$16.81	11.171%	$18.6878	$18.69	$18.70	$18.70
Purchase #6	$96.86	5.277%	$101.9713	$101.97	$101.95	$102.00
Purchase #7	$37.30	3.547%	$38.623	$38.62	$38.60	$38.60
7 purchase totals =	$498.40		$531.9328	$531.93	$531.85	$532.00