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	$56.62	5.662%	$59.8258	$59.83	$59.85	$59.80
Purchase #2	$225.60	3.427%	$233.3313	$233.33	$233.35	$233.30
Purchase #3	$204.87	6.230%	$217.6334	$217.63	$217.65	$217.60
Purchase #4	$57.82	7.481%	$62.1455	$62.15	$62.15	$62.10
Purchase #5	$92.43	6.635%	$98.5627	$98.56	$98.55	$98.60
Purchase #6	$240.95	5.153%	$253.3662	$253.37	$253.35	$253.40
Purchase #7	$147.29	10.583%	$162.8777	$162.88	$162.90	$162.90
7 purchase totals =	$1,025.58		$1,087.7426	$1,087.75	$1,087.80	$1,087.70