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	$155.84	6.428%	$165.8574	$165.86	$165.85	$165.90
Purchase #2	$138.93	10.458%	$153.4593	$153.46	$153.45	$153.50
Purchase #3	$32.79	4.835%	$34.3754	$34.38	$34.40	$34.40
Purchase #4	$249.72	5.438%	$263.2998	$263.30	$263.30	$263.30
Purchase #5	$16.25	12.470%	$18.2764	$18.28	$18.30	$18.30
Purchase #6	$136.89	12.160%	$153.5358	$153.54	$153.55	$153.50
Purchase #7	$99.98	12.350%	$112.3275	$112.33	$112.35	$112.30
7 purchase totals =	$830.40		$901.1316	$901.15	$901.20	$901.20