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	$51.97	5.856%	$55.0134	$55.01	$55.00	$55.00
Purchase #2	$81.38	9.708%	$89.2804	$89.28	$89.30	$89.30
Purchase #3	$32.39	9.436%	$35.4463	$35.45	$35.45	$35.40
Purchase #4	$117.33	8.293%	$127.0602	$127.06	$127.05	$127.10
Purchase #5	$142.41	4.299%	$148.5322	$148.53	$148.55	$148.50
Purchase #6	$124.86	8.434%	$135.3907	$135.39	$135.40	$135.40
Purchase #7	$52.74	9.646%	$57.8273	$57.83	$57.85	$57.80
7 purchase totals =	$603.08		$648.5505	$648.55	$648.60	$648.50