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	$217.38	3.746%	$225.5231	$225.52	$225.50	$225.50
Purchase #2	$151.85	10.188%	$167.3205	$167.32	$167.30	$167.30
Purchase #3	$79.77	4.216%	$83.1331	$83.13	$83.15	$83.10
Purchase #4	$90.60	10.698%	$100.2924	$100.29	$100.30	$100.30
Purchase #5	$7.40	12.561%	$8.3295	$8.33	$8.35	$8.30
Purchase #6	$228.98	12.591%	$257.8109	$257.81	$257.80	$257.80
Purchase #7	$34.77	10.738%	$38.5036	$38.50	$38.50	$38.50
7 purchase totals =	$810.75		$880.9131	$880.90	$880.90	$880.80