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	$31.58	9.755%	$34.6606	$34.66	$34.65	$34.70
Purchase #2	$128.28	7.828%	$138.3218	$138.32	$138.30	$138.30
Purchase #3	$78.44	13.539%	$89.06	$89.06	$89.05	$89.10
Purchase #4	$56.39	5.522%	$59.5039	$59.50	$59.50	$59.50
Purchase #5	$15.71	10.129%	$17.3013	$17.30	$17.30	$17.30
Purchase #6	$162.82	11.381%	$181.3505	$181.35	$181.35	$181.40
Purchase #7	$102.78	7.767%	$110.7629	$110.76	$110.75	$110.80
7 purchase totals =	$576.00		$630.9610	$630.95	$630.90	$631.10