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	$119.28	3.544%	$123.5073	$123.51	$123.50	$123.50
Purchase #2	$173.92	3.749%	$180.4403	$180.44	$180.45	$180.40
Purchase #3	$74.95	4.631%	$78.4209	$78.42	$78.40	$78.40
Purchase #4	$101.55	7.398%	$109.0627	$109.06	$109.05	$109.10
Purchase #5	$27.80	12.475%	$31.2681	$31.27	$31.25	$31.30
Purchase #6	$10.27	10.333%	$11.3312	$11.33	$11.35	$11.30
Purchase #7	$35.84	9.167%	$39.1255	$39.13	$39.15	$39.10
7 purchase totals =	$543.61		$573.1560	$573.16	$573.15	$573.10