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	$86.87	4.215%	$90.5316	$90.53	$90.55	$90.50
Purchase #2	$172.57	3.566%	$178.7238	$178.72	$178.70	$178.70
Purchase #3	$163.68	5.252%	$172.2765	$172.28	$172.30	$172.30
Purchase #4	$130.79	10.496%	$144.5177	$144.52	$144.50	$144.50
Purchase #5	$245.47	9.590%	$269.0106	$269.01	$269.00	$269.00
Purchase #6	$5.36	4.298%	$5.5904	$5.59	$5.60	$5.60
Purchase #7	$197.32	13.759%	$224.4693	$224.47	$224.45	$224.50
7 purchase totals =	$1,002.06		$1,085.1199	$1,085.12	$1,085.10	$1,085.10