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	$245.27	13.173%	$277.5794	$277.58	$277.60	$277.60
Purchase #2	$93.38	7.736%	$100.6039	$100.60	$100.60	$100.60
Purchase #3	$109.36	7.721%	$117.8037	$117.80	$117.80	$117.80
Purchase #4	$11.40	7.419%	$12.2458	$12.25	$12.25	$12.20
Purchase #5	$60.67	10.604%	$67.1034	$67.10	$67.10	$67.10
Purchase #6	$127.38	13.486%	$144.5585	$144.56	$144.55	$144.60
Purchase #7	$18.31	10.730%	$20.2747	$20.27	$20.25	$20.30
7 purchase totals =	$665.77		$740.1694	$740.16	$740.15	$740.20