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	$243.95	13.172%	$276.0831	$276.08	$276.10	$276.10
Purchase #2	$233.69	12.459%	$262.8054	$262.81	$262.80	$262.80
Purchase #3	$86.45	10.147%	$95.2221	$95.22	$95.20	$95.20
Purchase #4	$153.83	7.770%	$165.7826	$165.78	$165.80	$165.80
Purchase #5	$27.28	5.749%	$28.8483	$28.85	$28.85	$28.80
Purchase #6	$200.59	9.490%	$219.626	$219.63	$219.65	$219.60
Purchase #7	$25.89	5.147%	$27.2226	$27.22	$27.20	$27.20
7 purchase totals =	$971.68		$1,075.5901	$1,075.59	$1,075.60	$1,075.50