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	$41.30	3.473%	$42.7343	$42.73	$42.75	$42.70
Purchase #2	$161.59	11.704%	$180.5025	$180.50	$180.50	$180.50
Purchase #3	$225.60	11.823%	$252.2727	$252.27	$252.25	$252.30
Purchase #4	$214.77	5.172%	$225.8779	$225.88	$225.90	$225.90
Purchase #5	$56.71	4.371%	$59.1888	$59.19	$59.20	$59.20
Purchase #6	$206.86	4.410%	$215.9825	$215.98	$216.00	$216.00
Purchase #7	$36.70	5.563%	$38.7416	$38.74	$38.75	$38.70
7 purchase totals =	$943.53		$1,015.3003	$1,015.29	$1,015.35	$1,015.30