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	$18.40	13.310%	$20.849	$20.85	$20.85	$20.80
Purchase #2	$229.87	6.722%	$245.3219	$245.32	$245.30	$245.30
Purchase #3	$144.86	12.287%	$162.6589	$162.66	$162.65	$162.70
Purchase #4	$119.64	9.122%	$130.5536	$130.55	$130.55	$130.60
Purchase #5	$105.50	12.545%	$118.735	$118.74	$118.75	$118.70
Purchase #6	$123.81	11.183%	$137.6557	$137.66	$137.65	$137.70
Purchase #7	$95.35	10.589%	$105.4466	$105.45	$105.45	$105.40
7 purchase totals =	$837.43		$921.2207	$921.23	$921.20	$921.20