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	$34.88	6.573%	$37.1727	$37.17	$37.15	$37.20
Purchase #2	$87.39	3.621%	$90.5544	$90.55	$90.55	$90.60
Purchase #3	$134.79	3.163%	$139.0534	$139.05	$139.05	$139.10
Purchase #4	$115.46	7.677%	$124.3239	$124.32	$124.30	$124.30
Purchase #5	$108.31	9.762%	$118.8832	$118.88	$118.90	$118.90
Purchase #6	$120.40	6.841%	$128.6366	$128.64	$128.65	$128.60
Purchase #7	$36.44	9.808%	$40.014	$40.01	$40.00	$40.00
7 purchase totals =	$637.67		$678.6382	$678.62	$678.60	$678.70