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	$129.52	10.829%	$143.5457	$143.55	$143.55	$143.50
Purchase #2	$66.69	5.389%	$70.2839	$70.28	$70.30	$70.30
Purchase #3	$94.97	3.740%	$98.5219	$98.52	$98.50	$98.50
Purchase #4	$160.66	7.562%	$172.8091	$172.81	$172.80	$172.80
Purchase #5	$107.54	3.556%	$111.3641	$111.36	$111.35	$111.40
Purchase #6	$113.69	6.544%	$121.1299	$121.13	$121.15	$121.10
Purchase #7	$91.28	9.239%	$99.7134	$99.71	$99.70	$99.70
7 purchase totals =	$764.35		$817.3680	$817.36	$817.35	$817.30