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	$89.31	11.292%	$99.3949	$99.39	$99.40	$99.40
Purchase #2	$29.97	10.371%	$33.0782	$33.08	$33.10	$33.10
Purchase #3	$163.89	6.286%	$174.1921	$174.19	$174.20	$174.20
Purchase #4	$250.75	11.520%	$279.6364	$279.64	$279.65	$279.60
Purchase #5	$81.76	11.775%	$91.3872	$91.39	$91.40	$91.40
Purchase #6	$95.72	3.661%	$99.2243	$99.22	$99.20	$99.20
Purchase #7	$56.52	10.587%	$62.5038	$62.50	$62.50	$62.50
7 purchase totals =	$767.92		$839.4169	$839.41	$839.45	$839.40