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	$71.39	8.307%	$77.3204	$77.32	$77.30	$77.30
Purchase #2	$145.93	13.260%	$165.2803	$165.28	$165.30	$165.30
Purchase #3	$99.51	3.862%	$103.3531	$103.35	$103.35	$103.40
Purchase #4	$70.39	11.668%	$78.6031	$78.60	$78.60	$78.60
Purchase #5	$161.90	5.793%	$171.2789	$171.28	$171.30	$171.30
Purchase #6	$237.99	8.360%	$257.886	$257.89	$257.90	$257.90
Purchase #7	$92.42	5.643%	$97.6353	$97.64	$97.65	$97.60
7 purchase totals =	$879.53		$951.3571	$951.36	$951.40	$951.40