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	$139.47	13.194%	$157.8717	$157.87	$157.85	$157.90
Purchase #2	$116.76	3.713%	$121.0953	$121.10	$121.10	$121.10
Purchase #3	$110.96	10.874%	$123.0258	$123.03	$123.05	$123.00
Purchase #4	$17.61	11.215%	$19.585	$19.59	$19.60	$19.60
Purchase #5	$131.39	7.717%	$141.5294	$141.53	$141.55	$141.50
Purchase #6	$83.28	8.474%	$90.3371	$90.34	$90.35	$90.30
Purchase #7	$127.75	6.751%	$136.3744	$136.37	$136.35	$136.40
7 purchase totals =	$727.22		$789.8187	$789.83	$789.85	$789.80