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	$165.98	9.836%	$182.3058	$182.31	$182.30	$182.30
Purchase #2	$158.27	10.751%	$175.2856	$175.29	$175.30	$175.30
Purchase #3	$126.80	12.463%	$142.6031	$142.60	$142.60	$142.60
Purchase #4	$228.88	4.454%	$239.0743	$239.07	$239.05	$239.10
Purchase #5	$168.44	9.182%	$183.9062	$183.91	$183.90	$183.90
Purchase #6	$118.85	10.853%	$131.7488	$131.75	$131.75	$131.70
Purchase #7	$80.75	11.175%	$89.7738	$89.77	$89.75	$89.80
7 purchase totals =	$1,047.97		$1,144.6976	$1,144.70	$1,144.65	$1,144.70