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	$68.72	6.347%	$73.0817	$73.08	$73.10	$73.10
Purchase #2	$100.86	10.819%	$111.772	$111.77	$111.75	$111.80
Purchase #3	$230.75	5.473%	$243.3789	$243.38	$243.40	$243.40
Purchase #4	$108.27	5.136%	$113.8307	$113.83	$113.85	$113.80
Purchase #5	$85.71	8.353%	$92.8694	$92.87	$92.85	$92.90
Purchase #6	$15.71	9.523%	$17.2061	$17.21	$17.20	$17.20
Purchase #7	$195.49	13.592%	$222.061	$222.06	$222.05	$222.10
7 purchase totals =	$805.51		$874.1998	$874.20	$874.20	$874.30