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	$99.90	9.684%	$109.5743	$109.57	$109.55	$109.60
Purchase #2	$82.45	7.741%	$88.8325	$88.83	$88.85	$88.80
Purchase #3	$232.32	13.168%	$262.9119	$262.91	$262.90	$262.90
Purchase #4	$218.80	5.231%	$230.2454	$230.25	$230.25	$230.20
Purchase #5	$132.31	12.498%	$148.8461	$148.85	$148.85	$148.80
Purchase #6	$129.32	10.233%	$142.5533	$142.55	$142.55	$142.60
Purchase #7	$216.92	10.618%	$239.9526	$239.95	$239.95	$240.00
7 purchase totals =	$1,112.02		$1,222.9161	$1,222.91	$1,222.90	$1,222.90