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	$144.42	11.315%	$160.7611	$160.76	$160.75	$160.80
Purchase #2	$30.49	4.195%	$31.7691	$31.77	$31.75	$31.80
Purchase #3	$76.56	5.570%	$80.8244	$80.82	$80.80	$80.80
Purchase #4	$70.27	12.610%	$79.131	$79.13	$79.15	$79.10
Purchase #5	$42.73	5.336%	$45.0101	$45.01	$45.00	$45.00
Purchase #6	$90.54	9.445%	$99.0915	$99.09	$99.10	$99.10
Purchase #7	$76.94	8.483%	$83.4668	$83.47	$83.45	$83.50
7 purchase totals =	$531.95		$580.0540	$580.05	$580.00	$580.10