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	$80.64	11.227%	$89.6935	$89.69	$89.70	$89.70
Purchase #2	$187.29	9.451%	$204.9908	$204.99	$205.00	$205.00
Purchase #3	$167.33	7.494%	$179.8697	$179.87	$179.85	$179.90
Purchase #4	$56.85	4.396%	$59.3491	$59.35	$59.35	$59.30
Purchase #5	$100.83	13.282%	$114.2222	$114.22	$114.20	$114.20
Purchase #6	$75.55	11.810%	$84.4725	$84.47	$84.45	$84.50
Purchase #7	$138.51	8.841%	$150.7557	$150.76	$150.75	$150.80
7 purchase totals =	$807.00		$883.3535	$883.35	$883.30	$883.40