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	$228.76	5.279%	$240.8362	$240.84	$240.85	$240.80
Purchase #2	$140.48	11.167%	$156.1674	$156.17	$156.15	$156.20
Purchase #3	$167.47	5.560%	$176.7813	$176.78	$176.80	$176.80
Purchase #4	$217.29	11.130%	$241.4744	$241.47	$241.45	$241.50
Purchase #5	$129.45	8.849%	$140.905	$140.91	$140.90	$140.90
Purchase #6	$77.46	10.169%	$85.3369	$85.34	$85.35	$85.30
Purchase #7	$166.60	12.247%	$187.0035	$187.00	$187.00	$187.00
7 purchase totals =	$1,127.51		$1,228.5047	$1,228.51	$1,228.50	$1,228.50