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	$20.99	7.298%	$22.5219	$22.52	$22.50	$22.50
Purchase #2	$105.91	8.468%	$114.8785	$114.88	$114.90	$114.90
Purchase #3	$42.57	6.794%	$45.4622	$45.46	$45.45	$45.50
Purchase #4	$104.79	13.828%	$119.2804	$119.28	$119.30	$119.30
Purchase #5	$201.95	3.240%	$208.4932	$208.49	$208.50	$208.50
Purchase #6	$249.68	6.422%	$265.7144	$265.71	$265.70	$265.70
Purchase #7	$17.59	12.666%	$19.8179	$19.82	$19.80	$19.80
7 purchase totals =	$743.48		$796.1685	$796.16	$796.15	$796.20