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	$141.51	13.622%	$160.7865	$160.79	$160.80	$160.80
Purchase #2	$249.49	5.204%	$262.4735	$262.47	$262.45	$262.50
Purchase #3	$29.88	5.279%	$31.4574	$31.46	$31.45	$31.50
Purchase #4	$131.82	10.322%	$145.4265	$145.43	$145.45	$145.40
Purchase #5	$150.64	6.396%	$160.2749	$160.27	$160.25	$160.30
Purchase #6	$52.30	5.461%	$55.1561	$55.16	$55.15	$55.20
Purchase #7	$26.63	6.786%	$28.4371	$28.44	$28.45	$28.40
7 purchase totals =	$782.27		$844.0120	$844.02	$844.00	$844.10