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	$159.99	13.589%	$181.731	$181.73	$181.75	$181.70
Purchase #2	$40.31	8.314%	$43.6614	$43.66	$43.65	$43.70
Purchase #3	$83.58	8.650%	$90.8097	$90.81	$90.80	$90.80
Purchase #4	$152.74	6.712%	$162.9919	$162.99	$163.00	$163.00
Purchase #5	$64.94	11.805%	$72.6062	$72.61	$72.60	$72.60
Purchase #6	$71.75	10.843%	$79.5299	$79.53	$79.55	$79.50
Purchase #7	$48.26	10.482%	$53.3186	$53.32	$53.30	$53.30
7 purchase totals =	$621.57		$684.6487	$684.65	$684.65	$684.60