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	$202.57	7.554%	$217.8721	$217.87	$217.85	$217.90
Purchase #2	$137.91	9.314%	$150.7549	$150.75	$150.75	$150.80
Purchase #3	$146.91	10.463%	$162.2812	$162.28	$162.30	$162.30
Purchase #4	$146.42	4.274%	$152.678	$152.68	$152.70	$152.70
Purchase #5	$98.75	13.685%	$112.2639	$112.26	$112.25	$112.30
Purchase #6	$95.83	7.727%	$103.2348	$103.23	$103.25	$103.20
Purchase #7	$36.68	9.744%	$40.2541	$40.25	$40.25	$40.30
7 purchase totals =	$865.07		$939.3390	$939.32	$939.35	$939.50