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	$144.97	13.137%	$164.0147	$164.01	$164.00	$164.00
Purchase #2	$41.56	11.744%	$46.4408	$46.44	$46.45	$46.40
Purchase #3	$200.32	4.436%	$209.2062	$209.21	$209.20	$209.20
Purchase #4	$130.74	4.361%	$136.4416	$136.44	$136.45	$136.40
Purchase #5	$56.32	6.235%	$59.8316	$59.83	$59.85	$59.80
Purchase #6	$245.85	10.845%	$272.5124	$272.51	$272.50	$272.50
Purchase #7	$64.71	9.680%	$70.9739	$70.97	$70.95	$71.00
7 purchase totals =	$884.47		$959.4212	$959.41	$959.40	$959.30