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	$90.38	12.123%	$101.3368	$101.34	$101.35	$101.30
Purchase #2	$89.56	3.620%	$92.8021	$92.80	$92.80	$92.80
Purchase #3	$16.76	4.295%	$17.4798	$17.48	$17.50	$17.50
Purchase #4	$123.72	9.806%	$135.852	$135.85	$135.85	$135.90
Purchase #5	$126.58	11.474%	$141.1038	$141.10	$141.10	$141.10
Purchase #6	$115.83	10.386%	$127.8601	$127.86	$127.85	$127.90
Purchase #7	$214.53	11.371%	$238.9242	$238.92	$238.90	$238.90
7 purchase totals =	$777.36		$855.3588	$855.35	$855.35	$855.40