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	$29.42	10.366%	$32.4697	$32.47	$32.45	$32.50
Purchase #2	$171.90	10.772%	$190.4171	$190.42	$190.40	$190.40
Purchase #3	$245.37	4.731%	$256.9785	$256.98	$257.00	$257.00
Purchase #4	$137.53	11.573%	$153.4463	$153.45	$153.45	$153.40
Purchase #5	$35.95	6.660%	$38.3443	$38.34	$38.35	$38.30
Purchase #6	$82.33	5.812%	$87.115	$87.12	$87.10	$87.10
Purchase #7	$96.85	9.208%	$105.7679	$105.77	$105.75	$105.80
7 purchase totals =	$799.35		$864.5388	$864.55	$864.50	$864.50