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	$194.86	12.642%	$219.4942	$219.49	$219.50	$219.50
Purchase #2	$18.57	13.813%	$21.1351	$21.14	$21.15	$21.10
Purchase #3	$123.97	12.764%	$139.7935	$139.79	$139.80	$139.80
Purchase #4	$102.93	5.421%	$108.5098	$108.51	$108.50	$108.50
Purchase #5	$30.57	6.871%	$32.6705	$32.67	$32.65	$32.70
Purchase #6	$41.26	5.759%	$43.6362	$43.64	$43.65	$43.60
Purchase #7	$233.43	9.253%	$255.0293	$255.03	$255.05	$255.00
7 purchase totals =	$745.59		$820.2686	$820.27	$820.30	$820.20