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	$16.70	5.139%	$17.5582	$17.56	$17.55	$17.60
Purchase #2	$193.27	10.254%	$213.0879	$213.09	$213.10	$213.10
Purchase #3	$32.28	11.175%	$35.8873	$35.89	$35.90	$35.90
Purchase #4	$18.85	6.528%	$20.0805	$20.08	$20.10	$20.10
Purchase #5	$62.76	7.128%	$67.2335	$67.23	$67.25	$67.20
Purchase #6	$153.45	5.793%	$162.3394	$162.34	$162.35	$162.30
Purchase #7	$118.90	4.556%	$124.3171	$124.32	$124.30	$124.30
7 purchase totals =	$596.21		$640.5039	$640.51	$640.55	$640.50