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	$126.50	6.644%	$134.9047	$134.90	$134.90	$134.90
Purchase #2	$22.60	3.261%	$23.337	$23.34	$23.35	$23.30
Purchase #3	$112.40	5.394%	$118.4629	$118.46	$118.45	$118.50
Purchase #4	$66.65	11.394%	$74.2441	$74.24	$74.25	$74.20
Purchase #5	$167.91	11.654%	$187.4782	$187.48	$187.50	$187.50
Purchase #6	$82.64	8.792%	$89.9057	$89.91	$89.90	$89.90
Purchase #7	$62.77	4.444%	$65.5595	$65.56	$65.55	$65.60
7 purchase totals =	$641.47		$693.8921	$693.89	$693.90	$693.90