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	$9.28	5.874%	$9.8251	$9.83	$9.85	$9.80
Purchase #2	$55.82	13.275%	$63.2301	$63.23	$63.25	$63.20
Purchase #3	$112.46	9.479%	$123.1201	$123.12	$123.10	$123.10
Purchase #4	$29.32	11.232%	$32.6132	$32.61	$32.60	$32.60
Purchase #5	$79.31	9.374%	$86.7445	$86.74	$86.75	$86.70
Purchase #6	$95.58	8.735%	$103.9289	$103.93	$103.95	$103.90
Purchase #7	$95.80	5.380%	$100.954	$100.95	$100.95	$101.00
7 purchase totals =	$477.57		$520.4159	$520.41	$520.45	$520.30