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	$21.35	5.107%	$22.4403	$22.44	$22.45	$22.40
Purchase #2	$160.47	4.143%	$167.1183	$167.12	$167.10	$167.10
Purchase #3	$109.42	12.490%	$123.0866	$123.09	$123.10	$123.10
Purchase #4	$128.35	4.601%	$134.2554	$134.26	$134.25	$134.30
Purchase #5	$39.33	3.377%	$40.6582	$40.66	$40.65	$40.70
Purchase #6	$76.30	13.728%	$86.7745	$86.77	$86.75	$86.80
Purchase #7	$151.78	6.419%	$161.5228	$161.52	$161.50	$161.50
7 purchase totals =	$687.00		$735.8561	$735.86	$735.80	$735.90