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	$168.87	11.649%	$188.5417	$188.54	$188.55	$188.50
Purchase #2	$141.68	4.855%	$148.5586	$148.56	$148.55	$148.60
Purchase #3	$103.61	5.699%	$109.5147	$109.51	$109.50	$109.50
Purchase #4	$229.77	9.654%	$251.952	$251.95	$251.95	$252.00
Purchase #5	$87.31	10.234%	$96.2453	$96.25	$96.25	$96.20
Purchase #6	$94.56	9.376%	$103.4259	$103.43	$103.45	$103.40
Purchase #7	$36.30	5.867%	$38.4297	$38.43	$38.45	$38.40
7 purchase totals =	$862.10		$936.6679	$936.67	$936.70	$936.60