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	$86.44	5.183%	$90.9202	$90.92	$90.90	$90.90
Purchase #2	$84.55	5.680%	$89.3524	$89.35	$89.35	$89.40
Purchase #3	$132.57	9.598%	$145.2941	$145.29	$145.30	$145.30
Purchase #4	$169.50	11.278%	$188.6162	$188.62	$188.60	$188.60
Purchase #5	$185.96	6.487%	$198.0232	$198.02	$198.00	$198.00
Purchase #6	$49.90	10.357%	$55.0681	$55.07	$55.05	$55.10
Purchase #7	$129.82	12.541%	$146.1007	$146.10	$146.10	$146.10
7 purchase totals =	$838.74		$913.3749	$913.37	$913.30	$913.40