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	$50.71	11.225%	$56.4022	$56.40	$56.40	$56.40
Purchase #2	$143.95	12.136%	$161.4198	$161.42	$161.40	$161.40
Purchase #3	$116.91	9.245%	$127.7183	$127.72	$127.70	$127.70
Purchase #4	$93.95	10.764%	$104.0628	$104.06	$104.05	$104.10
Purchase #5	$78.93	8.251%	$85.4425	$85.44	$85.45	$85.40
Purchase #6	$91.64	12.240%	$102.8567	$102.86	$102.85	$102.90
Purchase #7	$108.27	4.734%	$113.3955	$113.40	$113.40	$113.40
7 purchase totals =	$684.36		$751.2978	$751.30	$751.25	$751.30