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	$52.96	12.337%	$59.4937	$59.49	$59.50	$59.50
Purchase #2	$214.32	6.724%	$228.7309	$228.73	$228.75	$228.70
Purchase #3	$189.79	7.751%	$204.5006	$204.50	$204.50	$204.50
Purchase #4	$207.55	6.155%	$220.3247	$220.32	$220.30	$220.30
Purchase #5	$29.83	12.593%	$33.5865	$33.59	$33.60	$33.60
Purchase #6	$116.85	12.112%	$131.0029	$131.00	$131.00	$131.00
Purchase #7	$94.51	6.205%	$100.3743	$100.37	$100.35	$100.40
7 purchase totals =	$905.81		$978.0136	$978.00	$978.00	$978.00