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	$83.45	3.678%	$86.5193	$86.52	$86.50	$86.50
Purchase #2	$247.66	4.140%	$257.9131	$257.91	$257.90	$257.90
Purchase #3	$159.37	6.348%	$169.4868	$169.49	$169.50	$169.50
Purchase #4	$185.89	3.493%	$192.3831	$192.38	$192.40	$192.40
Purchase #5	$169.58	4.159%	$176.6328	$176.63	$176.65	$176.60
Purchase #6	$244.95	13.775%	$278.6919	$278.69	$278.70	$278.70
Purchase #7	$36.69	7.164%	$39.3185	$39.32	$39.30	$39.30
7 purchase totals =	$1,127.59		$1,200.9455	$1,200.94	$1,200.95	$1,200.90