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	$15.72	10.831%	$17.4226	$17.42	$17.40	$17.40
Purchase #2	$175.44	9.166%	$191.5208	$191.52	$191.50	$191.50
Purchase #3	$123.53	12.615%	$139.1133	$139.11	$139.10	$139.10
Purchase #4	$166.36	10.285%	$183.4701	$183.47	$183.45	$183.50
Purchase #5	$192.33	8.744%	$209.1473	$209.15	$209.15	$209.10
Purchase #6	$103.32	10.860%	$114.5406	$114.54	$114.55	$114.50
Purchase #7	$75.60	4.182%	$78.7616	$78.76	$78.75	$78.80
7 purchase totals =	$852.30		$933.9763	$933.97	$933.90	$933.90