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	$55.32	11.859%	$61.8804	$61.88	$61.90	$61.90
Purchase #2	$116.94	4.114%	$121.7509	$121.75	$121.75	$121.80
Purchase #3	$8.85	12.117%	$9.9224	$9.92	$9.90	$9.90
Purchase #4	$59.35	12.523%	$66.7824	$66.78	$66.80	$66.80
Purchase #5	$99.64	10.293%	$109.8959	$109.90	$109.90	$109.90
Purchase #6	$29.27	7.831%	$31.5621	$31.56	$31.55	$31.60
Purchase #7	$103.98	4.212%	$108.3596	$108.36	$108.35	$108.40
7 purchase totals =	$473.35		$510.1537	$510.15	$510.15	$510.30