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	$115.34	4.104%	$120.0736	$120.07	$120.05	$120.10
Purchase #2	$33.41	11.243%	$37.1663	$37.17	$37.15	$37.20
Purchase #3	$31.27	4.371%	$32.6368	$32.64	$32.65	$32.60
Purchase #4	$95.96	10.385%	$105.9254	$105.93	$105.95	$105.90
Purchase #5	$112.49	6.172%	$119.4329	$119.43	$119.45	$119.40
Purchase #6	$14.80	4.472%	$15.4619	$15.46	$15.45	$15.50
Purchase #7	$200.36	5.569%	$211.518	$211.52	$211.50	$211.50
7 purchase totals =	$603.63		$642.2149	$642.22	$642.20	$642.20