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	$156.86	8.665%	$170.4519	$170.45	$170.45	$170.50
Purchase #2	$13.68	10.410%	$15.1041	$15.10	$15.10	$15.10
Purchase #3	$158.75	8.596%	$172.3962	$172.40	$172.40	$172.40
Purchase #4	$194.25	7.854%	$209.5064	$209.51	$209.50	$209.50
Purchase #5	$85.27	6.598%	$90.8961	$90.90	$90.90	$90.90
Purchase #6	$81.46	7.188%	$87.3153	$87.32	$87.30	$87.30
Purchase #7	$68.47	12.625%	$77.1143	$77.11	$77.10	$77.10
7 purchase totals =	$758.74		$822.7843	$822.79	$822.75	$822.80