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	$22.52	6.504%	$23.9847	$23.98	$24.00	$24.00
Purchase #2	$56.26	6.246%	$59.774	$59.77	$59.75	$59.80
Purchase #3	$83.55	7.462%	$89.7845	$89.78	$89.80	$89.80
Purchase #4	$158.32	5.141%	$166.4592	$166.46	$166.45	$166.50
Purchase #5	$209.80	4.326%	$218.8759	$218.88	$218.90	$218.90
Purchase #6	$206.44	5.560%	$217.9181	$217.92	$217.90	$217.90
Purchase #7	$41.99	11.287%	$46.7294	$46.73	$46.75	$46.70
7 purchase totals =	$778.88		$823.5258	$823.52	$823.55	$823.60