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	$100.31	11.446%	$111.7915	$111.79	$111.80	$111.80
Purchase #2	$38.67	10.610%	$42.7729	$42.77	$42.75	$42.80
Purchase #3	$199.27	3.400%	$206.0452	$206.05	$206.05	$206.00
Purchase #4	$87.65	12.707%	$98.7877	$98.79	$98.80	$98.80
Purchase #5	$73.80	12.337%	$82.9047	$82.90	$82.90	$82.90
Purchase #6	$70.60	12.709%	$79.5726	$79.57	$79.55	$79.60
Purchase #7	$7.25	12.634%	$8.166	$8.17	$8.15	$8.20
7 purchase totals =	$577.55		$630.0406	$630.04	$630.00	$630.10