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	$171.98	5.121%	$180.7871	$180.79	$180.80	$180.80
Purchase #2	$124.53	11.469%	$138.8123	$138.81	$138.80	$138.80
Purchase #3	$83.56	5.837%	$88.4374	$88.44	$88.45	$88.40
Purchase #4	$99.56	4.358%	$103.8988	$103.90	$103.90	$103.90
Purchase #5	$45.37	11.861%	$50.7513	$50.75	$50.75	$50.80
Purchase #6	$153.92	7.581%	$165.5887	$165.59	$165.60	$165.60
Purchase #7	$206.79	7.705%	$222.7232	$222.72	$222.70	$222.70
7 purchase totals =	$885.71		$950.9988	$951.00	$951.00	$951.00