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	$248.62	11.242%	$276.5699	$276.57	$276.55	$276.60
Purchase #2	$207.77	10.738%	$230.0803	$230.08	$230.10	$230.10
Purchase #3	$88.83	13.489%	$100.8123	$100.81	$100.80	$100.80
Purchase #4	$11.98	4.120%	$12.4736	$12.47	$12.45	$12.50
Purchase #5	$37.29	12.237%	$41.8532	$41.85	$41.85	$41.90
Purchase #6	$143.96	4.820%	$150.8989	$150.90	$150.90	$150.90
Purchase #7	$86.85	13.269%	$98.3741	$98.37	$98.35	$98.40
7 purchase totals =	$825.30		$911.0623	$911.05	$911.00	$911.20