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	$35.47	9.286%	$38.7637	$38.76	$38.75	$38.80
Purchase #2	$135.51	4.679%	$141.8505	$141.85	$141.85	$141.90
Purchase #3	$52.86	7.350%	$56.7452	$56.75	$56.75	$56.70
Purchase #4	$32.93	13.586%	$37.4039	$37.40	$37.40	$37.40
Purchase #5	$151.82	4.290%	$158.3331	$158.33	$158.35	$158.30
Purchase #6	$128.53	8.658%	$139.6581	$139.66	$139.65	$139.70
Purchase #7	$220.35	9.501%	$241.2855	$241.29	$241.30	$241.30
7 purchase totals =	$757.47		$814.0400	$814.04	$814.05	$814.10