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	$77.34	8.406%	$83.8412	$83.84	$83.85	$83.80
Purchase #2	$74.60	7.637%	$80.2972	$80.30	$80.30	$80.30
Purchase #3	$144.89	4.758%	$151.7839	$151.78	$151.80	$151.80
Purchase #4	$78.29	4.173%	$81.557	$81.56	$81.55	$81.60
Purchase #5	$165.44	5.422%	$174.4102	$174.41	$174.40	$174.40
Purchase #6	$151.72	13.346%	$171.9686	$171.97	$171.95	$172.00
Purchase #7	$105.92	10.778%	$117.3361	$117.34	$117.35	$117.30
7 purchase totals =	$798.20		$861.1942	$861.20	$861.20	$861.20