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	$226.93	6.780%	$242.3159	$242.32	$242.30	$242.30
Purchase #2	$37.33	4.154%	$38.8807	$38.88	$38.90	$38.90
Purchase #3	$33.38	9.631%	$36.5948	$36.59	$36.60	$36.60
Purchase #4	$99.82	8.411%	$108.2159	$108.22	$108.20	$108.20
Purchase #5	$26.54	5.182%	$27.9153	$27.92	$27.90	$27.90
Purchase #6	$77.30	11.116%	$85.8927	$85.89	$85.90	$85.90
Purchase #7	$95.42	12.656%	$107.4964	$107.50	$107.50	$107.50
7 purchase totals =	$596.72		$647.3117	$647.32	$647.30	$647.30