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	$72.56	8.214%	$78.5201	$78.52	$78.50	$78.50
Purchase #2	$208.80	6.715%	$222.8209	$222.82	$222.80	$222.80
Purchase #3	$22.93	9.608%	$25.1331	$25.13	$25.15	$25.10
Purchase #4	$63.56	4.358%	$66.3299	$66.33	$66.35	$66.30
Purchase #5	$79.42	7.351%	$85.2582	$85.26	$85.25	$85.30
Purchase #6	$192.61	10.452%	$212.7416	$212.74	$212.75	$212.70
Purchase #7	$108.95	9.108%	$118.8732	$118.87	$118.85	$118.90
7 purchase totals =	$748.83		$809.6770	$809.67	$809.65	$809.60