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	$66.71	13.265%	$75.5591	$75.56	$75.55	$75.60
Purchase #2	$117.93	6.253%	$125.3042	$125.30	$125.30	$125.30
Purchase #3	$47.30	11.276%	$52.6335	$52.63	$52.65	$52.60
Purchase #4	$85.67	4.440%	$89.4737	$89.47	$89.45	$89.50
Purchase #5	$150.33	5.417%	$158.4734	$158.47	$158.45	$158.50
Purchase #6	$12.85	4.153%	$13.3837	$13.38	$13.40	$13.40
Purchase #7	$100.49	7.647%	$108.1745	$108.17	$108.15	$108.20
7 purchase totals =	$581.28		$623.0021	$622.98	$622.95	$623.10