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	$10.90	6.406%	$11.5983	$11.60	$11.60	$11.60
Purchase #2	$155.97	9.328%	$170.5189	$170.52	$170.50	$170.50
Purchase #3	$73.59	11.631%	$82.1493	$82.15	$82.15	$82.10
Purchase #4	$188.98	12.728%	$213.0334	$213.03	$213.05	$213.00
Purchase #5	$244.81	4.534%	$255.9097	$255.91	$255.90	$255.90
Purchase #6	$167.42	13.136%	$189.4123	$189.41	$189.40	$189.40
Purchase #7	$15.86	10.711%	$17.5588	$17.56	$17.55	$17.60
7 purchase totals =	$857.53		$940.1807	$940.18	$940.15	$940.10