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	$116.50	3.397%	$120.4575	$120.46	$120.45	$120.50
Purchase #2	$158.49	3.660%	$164.2907	$164.29	$164.30	$164.30
Purchase #3	$16.33	13.306%	$18.5029	$18.50	$18.50	$18.50
Purchase #4	$99.64	5.774%	$105.3932	$105.39	$105.40	$105.40
Purchase #5	$52.38	5.874%	$55.4568	$55.46	$55.45	$55.50
Purchase #6	$36.68	7.784%	$39.5352	$39.54	$39.55	$39.50
Purchase #7	$24.95	7.182%	$26.7419	$26.74	$26.75	$26.70
7 purchase totals =	$504.97		$530.3782	$530.38	$530.40	$530.40