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	$17.38	6.591%	$18.5255	$18.53	$18.55	$18.50
Purchase #2	$169.79	5.552%	$179.2167	$179.22	$179.20	$179.20
Purchase #3	$188.27	4.365%	$196.488	$196.49	$196.50	$196.50
Purchase #4	$52.25	6.450%	$55.6201	$55.62	$55.60	$55.60
Purchase #5	$105.45	4.823%	$110.5359	$110.54	$110.55	$110.50
Purchase #6	$113.63	12.788%	$128.161	$128.16	$128.15	$128.20
Purchase #7	$101.66	9.564%	$111.3828	$111.38	$111.40	$111.40
7 purchase totals =	$748.43		$799.9300	$799.94	$799.95	$799.90