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	$123.41	9.213%	$134.7798	$134.78	$134.80	$134.80
Purchase #2	$31.52	9.495%	$34.5128	$34.51	$34.50	$34.50
Purchase #3	$132.51	13.553%	$150.4691	$150.47	$150.45	$150.50
Purchase #4	$202.64	3.328%	$209.3839	$209.38	$209.40	$209.40
Purchase #5	$181.90	3.625%	$188.4939	$188.49	$188.50	$188.50
Purchase #6	$31.62	4.244%	$32.962	$32.96	$32.95	$33.00
Purchase #7	$56.64	3.866%	$58.8297	$58.83	$58.85	$58.80
7 purchase totals =	$760.24		$809.4312	$809.42	$809.45	$809.50