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	$112.91	9.348%	$123.4648	$123.46	$123.45	$123.50
Purchase #2	$86.42	3.165%	$89.1552	$89.16	$89.15	$89.20
Purchase #3	$109.51	7.315%	$117.5207	$117.52	$117.50	$117.50
Purchase #4	$16.83	4.243%	$17.5441	$17.54	$17.55	$17.50
Purchase #5	$145.87	11.806%	$163.0914	$163.09	$163.10	$163.10
Purchase #6	$179.63	11.681%	$200.6126	$200.61	$200.60	$200.60
Purchase #7	$106.32	3.268%	$109.7945	$109.79	$109.80	$109.80
7 purchase totals =	$757.49		$821.1833	$821.17	$821.15	$821.20