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	$109.86	13.670%	$124.8779	$124.88	$124.90	$124.90
Purchase #2	$163.58	11.454%	$182.3165	$182.32	$182.30	$182.30
Purchase #3	$226.69	3.104%	$233.7265	$233.73	$233.75	$233.70
Purchase #4	$111.44	10.597%	$123.2493	$123.25	$123.25	$123.20
Purchase #5	$39.61	13.170%	$44.8266	$44.83	$44.85	$44.80
Purchase #6	$134.85	6.234%	$143.2565	$143.26	$143.25	$143.30
Purchase #7	$151.99	9.606%	$166.5902	$166.59	$166.60	$166.60
7 purchase totals =	$938.02		$1,018.8435	$1,018.86	$1,018.90	$1,018.80