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	$94.46	6.155%	$100.274	$100.27	$100.25	$100.30
Purchase #2	$84.37	7.273%	$90.5062	$90.51	$90.50	$90.50
Purchase #3	$217.77	9.500%	$238.4582	$238.46	$238.45	$238.50
Purchase #4	$150.27	6.569%	$160.1412	$160.14	$160.15	$160.10
Purchase #5	$114.46	10.393%	$126.3558	$126.36	$126.35	$126.40
Purchase #6	$168.66	4.844%	$176.8299	$176.83	$176.85	$176.80
Purchase #7	$185.25	7.744%	$199.5958	$199.60	$199.60	$199.60
7 purchase totals =	$1,015.24		$1,092.1611	$1,092.17	$1,092.15	$1,092.20