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	$242.36	5.835%	$256.5017	$256.50	$256.50	$256.50
Purchase #2	$127.97	10.412%	$141.2942	$141.29	$141.30	$141.30
Purchase #3	$112.66	4.858%	$118.133	$118.13	$118.15	$118.10
Purchase #4	$30.41	10.659%	$33.6514	$33.65	$33.65	$33.70
Purchase #5	$92.91	11.205%	$103.3206	$103.32	$103.30	$103.30
Purchase #6	$53.32	5.672%	$56.3443	$56.34	$56.35	$56.30
Purchase #7	$212.33	4.575%	$222.0441	$222.04	$222.05	$222.00
7 purchase totals =	$871.96		$931.2893	$931.27	$931.30	$931.20