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	$84.99	4.816%	$89.0831	$89.08	$89.10	$89.10
Purchase #2	$74.69	11.223%	$83.0725	$83.07	$83.05	$83.10
Purchase #3	$122.42	5.302%	$128.9107	$128.91	$128.90	$128.90
Purchase #4	$142.38	10.172%	$156.8629	$156.86	$156.85	$156.90
Purchase #5	$169.62	10.166%	$186.8636	$186.86	$186.85	$186.90
Purchase #6	$203.85	10.772%	$225.8087	$225.81	$225.80	$225.80
Purchase #7	$111.47	13.443%	$126.4549	$126.45	$126.45	$126.50
7 purchase totals =	$909.42		$997.0564	$997.04	$997.00	$997.20