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	$83.87	8.139%	$90.6962	$90.70	$90.70	$90.70
Purchase #2	$52.74	6.656%	$56.2504	$56.25	$56.25	$56.30
Purchase #3	$208.70	13.824%	$237.5507	$237.55	$237.55	$237.60
Purchase #4	$167.32	12.523%	$188.2735	$188.27	$188.25	$188.30
Purchase #5	$112.41	9.728%	$123.3452	$123.35	$123.35	$123.30
Purchase #6	$21.47	4.486%	$22.4331	$22.43	$22.45	$22.40
Purchase #7	$60.56	10.185%	$66.728	$66.73	$66.75	$66.70
7 purchase totals =	$707.07		$785.2771	$785.28	$785.30	$785.30