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	$185.42	5.838%	$196.2448	$196.24	$196.25	$196.20
Purchase #2	$64.95	8.390%	$70.3993	$70.40	$70.40	$70.40
Purchase #3	$118.90	8.217%	$128.67	$128.67	$128.65	$128.70
Purchase #4	$116.91	6.114%	$124.0579	$124.06	$124.05	$124.10
Purchase #5	$125.94	4.581%	$131.7093	$131.71	$131.70	$131.70
Purchase #6	$16.43	3.725%	$17.042	$17.04	$17.05	$17.00
Purchase #7	$154.86	11.328%	$172.4025	$172.40	$172.40	$172.40
7 purchase totals =	$783.41		$840.5258	$840.52	$840.50	$840.50