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	$142.63	5.523%	$150.5075	$150.51	$150.50	$150.50
Purchase #2	$20.72	5.169%	$21.791	$21.79	$21.80	$21.80
Purchase #3	$175.34	8.433%	$190.1264	$190.13	$190.15	$190.10
Purchase #4	$55.38	11.445%	$61.7182	$61.72	$61.70	$61.70
Purchase #5	$195.75	7.581%	$210.5898	$210.59	$210.60	$210.60
Purchase #6	$113.42	5.162%	$119.2747	$119.27	$119.25	$119.30
Purchase #7	$77.66	4.109%	$80.851	$80.85	$80.85	$80.90
7 purchase totals =	$780.90		$834.8586	$834.86	$834.85	$834.90