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	$61.41	9.120%	$67.0106	$67.01	$67.00	$67.00
Purchase #2	$64.68	5.348%	$68.1391	$68.14	$68.15	$68.10
Purchase #3	$83.66	7.559%	$89.9839	$89.98	$90.00	$90.00
Purchase #4	$49.68	7.601%	$53.4562	$53.46	$53.45	$53.50
Purchase #5	$70.41	4.769%	$73.7679	$73.77	$73.75	$73.80
Purchase #6	$104.88	8.742%	$114.0486	$114.05	$114.05	$114.00
Purchase #7	$130.25	10.147%	$143.4665	$143.47	$143.45	$143.50
7 purchase totals =	$564.97		$609.8728	$609.88	$609.85	$609.90