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	$122.69	3.123%	$126.5216	$126.52	$126.50	$126.50
Purchase #2	$100.90	11.277%	$112.2785	$112.28	$112.30	$112.30
Purchase #3	$185.30	13.692%	$210.6713	$210.67	$210.65	$210.70
Purchase #4	$249.42	12.469%	$280.5202	$280.52	$280.50	$280.50
Purchase #5	$54.94	9.443%	$60.128	$60.13	$60.15	$60.10
Purchase #6	$95.46	11.215%	$106.1658	$106.17	$106.15	$106.20
Purchase #7	$173.58	10.318%	$191.49	$191.49	$191.50	$191.50
7 purchase totals =	$982.29		$1,087.7754	$1,087.78	$1,087.75	$1,087.80