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	$19.72	3.693%	$20.4483	$20.45	$20.45	$20.40
Purchase #2	$103.67	13.497%	$117.6623	$117.66	$117.65	$117.70
Purchase #3	$97.90	12.160%	$109.8046	$109.80	$109.80	$109.80
Purchase #4	$52.79	11.810%	$59.0245	$59.02	$59.00	$59.00
Purchase #5	$17.80	13.319%	$20.1708	$20.17	$20.15	$20.20
Purchase #6	$52.88	3.679%	$54.8255	$54.83	$54.85	$54.80
Purchase #7	$242.84	9.838%	$266.7306	$266.73	$266.75	$266.70
7 purchase totals =	$587.60		$648.6666	$648.66	$648.65	$648.60