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	$54.63	3.756%	$56.6819	$56.68	$56.70	$56.70
Purchase #2	$222.75	12.745%	$251.1395	$251.14	$251.15	$251.10
Purchase #3	$157.34	6.493%	$167.5561	$167.56	$167.55	$167.60
Purchase #4	$50.42	6.386%	$53.6398	$53.64	$53.65	$53.60
Purchase #5	$198.55	13.483%	$225.3205	$225.32	$225.30	$225.30
Purchase #6	$94.35	5.808%	$99.8298	$99.83	$99.85	$99.80
Purchase #7	$209.43	12.109%	$234.7899	$234.79	$234.80	$234.80
7 purchase totals =	$987.47		$1,088.9575	$1,088.96	$1,089.00	$1,088.90