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	$89.83	11.336%	$100.0131	$100.01	$100.00	$100.00
Purchase #2	$79.60	12.617%	$89.6431	$89.64	$89.65	$89.60
Purchase #3	$18.41	13.427%	$20.8819	$20.88	$20.90	$20.90
Purchase #4	$219.57	9.334%	$240.0647	$240.06	$240.05	$240.10
Purchase #5	$23.43	4.723%	$24.5366	$24.54	$24.55	$24.50
Purchase #6	$144.43	12.485%	$162.4621	$162.46	$162.45	$162.50
Purchase #7	$66.27	13.561%	$75.2569	$75.26	$75.25	$75.30
7 purchase totals =	$641.54		$712.8584	$712.85	$712.85	$712.90