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	$9.28	8.311%	$10.0513	$10.05	$10.05	$10.10
Purchase #2	$174.82	12.612%	$196.8683	$196.87	$196.85	$196.90
Purchase #3	$83.81	9.725%	$91.9605	$91.96	$91.95	$92.00
Purchase #4	$110.54	4.288%	$115.28	$115.28	$115.30	$115.30
Purchase #5	$63.27	12.384%	$71.1054	$71.11	$71.10	$71.10
Purchase #6	$19.85	3.294%	$20.5039	$20.50	$20.50	$20.50
Purchase #7	$188.61	12.852%	$212.8502	$212.85	$212.85	$212.90
7 purchase totals =	$650.18		$718.6196	$718.62	$718.60	$718.80