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	$28.93	12.437%	$32.528	$32.53	$32.55	$32.50
Purchase #2	$41.52	10.774%	$45.9934	$45.99	$46.00	$46.00
Purchase #3	$194.94	13.449%	$221.1575	$221.16	$221.15	$221.20
Purchase #4	$208.88	9.111%	$227.9111	$227.91	$227.90	$227.90
Purchase #5	$153.32	12.727%	$172.833	$172.83	$172.85	$172.80
Purchase #6	$54.44	8.525%	$59.081	$59.08	$59.10	$59.10
Purchase #7	$229.34	4.849%	$240.4607	$240.46	$240.45	$240.50
7 purchase totals =	$911.37		$999.9647	$999.96	$1,000.00	$1,000.00