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	$25.93	11.343%	$28.8712	$28.87	$28.85	$28.90
Purchase #2	$71.51	11.572%	$79.7851	$79.79	$79.80	$79.80
Purchase #3	$160.42	3.778%	$166.4807	$166.48	$166.50	$166.50
Purchase #4	$45.80	9.694%	$50.2399	$50.24	$50.25	$50.20
Purchase #5	$45.80	10.803%	$50.7478	$50.75	$50.75	$50.70
Purchase #6	$82.33	8.706%	$89.4976	$89.50	$89.50	$89.50
Purchase #7	$91.37	12.144%	$102.466	$102.47	$102.45	$102.50
7 purchase totals =	$523.16		$568.0883	$568.10	$568.10	$568.10