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	$113.83	9.247%	$124.3559	$124.36	$124.35	$124.40
Purchase #2	$42.98	3.463%	$44.4684	$44.47	$44.45	$44.50
Purchase #3	$187.69	6.576%	$200.0325	$200.03	$200.05	$200.00
Purchase #4	$124.87	11.734%	$139.5222	$139.52	$139.50	$139.50
Purchase #5	$70.60	13.442%	$80.0901	$80.09	$80.10	$80.10
Purchase #6	$139.56	7.675%	$150.2712	$150.27	$150.25	$150.30
Purchase #7	$152.81	13.201%	$172.9824	$172.98	$173.00	$173.00
7 purchase totals =	$832.34		$911.7227	$911.72	$911.70	$911.80