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	$42.26	12.114%	$47.3794	$47.38	$47.40	$47.40
Purchase #2	$26.71	9.606%	$29.2758	$29.28	$29.30	$29.30
Purchase #3	$179.47	6.856%	$191.7745	$191.77	$191.75	$191.80
Purchase #4	$142.98	9.510%	$156.5774	$156.58	$156.60	$156.60
Purchase #5	$144.91	5.686%	$153.1496	$153.15	$153.15	$153.10
Purchase #6	$160.55	12.667%	$180.8869	$180.89	$180.90	$180.90
Purchase #7	$40.85	5.191%	$42.9705	$42.97	$42.95	$43.00
7 purchase totals =	$737.73		$802.0141	$802.02	$802.05	$802.10