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	$109.32	13.654%	$124.2466	$124.25	$124.25	$124.20
Purchase #2	$100.54	8.805%	$109.3925	$109.39	$109.40	$109.40
Purchase #3	$153.31	10.777%	$169.8322	$169.83	$169.85	$169.80
Purchase #4	$20.55	9.572%	$22.517	$22.52	$22.50	$22.50
Purchase #5	$89.66	10.632%	$99.1927	$99.19	$99.20	$99.20
Purchase #6	$24.90	12.521%	$28.0177	$28.02	$28.00	$28.00
Purchase #7	$210.46	13.382%	$238.6238	$238.62	$238.60	$238.60
7 purchase totals =	$708.74		$791.8225	$791.82	$791.80	$791.70