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	$39.28	5.858%	$41.581	$41.58	$41.60	$41.60
Purchase #2	$91.81	12.538%	$103.3211	$103.32	$103.30	$103.30
Purchase #3	$189.43	13.749%	$215.4747	$215.47	$215.45	$215.50
Purchase #4	$79.83	11.732%	$89.1957	$89.20	$89.20	$89.20
Purchase #5	$90.65	4.672%	$94.8852	$94.89	$94.90	$94.90
Purchase #6	$10.40	6.752%	$11.1022	$11.10	$11.10	$11.10
Purchase #7	$159.63	12.205%	$179.1128	$179.11	$179.10	$179.10
7 purchase totals =	$661.03		$734.6727	$734.67	$734.65	$734.70