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	$140.84	12.688%	$158.7098	$158.71	$158.70	$158.70
Purchase #2	$179.67	5.620%	$189.7675	$189.77	$189.75	$189.80
Purchase #3	$26.54	6.856%	$28.3596	$28.36	$28.35	$28.40
Purchase #4	$100.93	10.234%	$111.2592	$111.26	$111.25	$111.30
Purchase #5	$66.81	3.654%	$69.2512	$69.25	$69.25	$69.30
Purchase #6	$173.89	10.742%	$192.5693	$192.57	$192.55	$192.60
Purchase #7	$213.36	7.170%	$228.6579	$228.66	$228.65	$228.70
7 purchase totals =	$902.04		$978.5745	$978.58	$978.50	$978.80