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	$72.59	9.430%	$79.4352	$79.44	$79.45	$79.40
Purchase #2	$58.85	10.233%	$64.8721	$64.87	$64.85	$64.90
Purchase #3	$181.33	10.792%	$200.8991	$200.90	$200.90	$200.90
Purchase #4	$137.74	9.535%	$150.8735	$150.87	$150.85	$150.90
Purchase #5	$249.31	5.572%	$263.2016	$263.20	$263.20	$263.20
Purchase #6	$57.66	13.456%	$65.4187	$65.42	$65.40	$65.40
Purchase #7	$42.58	8.250%	$46.0929	$46.09	$46.10	$46.10
7 purchase totals =	$800.06		$870.7931	$870.79	$870.75	$870.80