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	$183.56	4.659%	$192.1121	$192.11	$192.10	$192.10
Purchase #2	$116.73	13.400%	$132.3718	$132.37	$132.35	$132.40
Purchase #3	$142.45	6.598%	$151.8489	$151.85	$151.85	$151.80
Purchase #4	$138.41	12.297%	$155.4303	$155.43	$155.45	$155.40
Purchase #5	$49.33	5.257%	$51.9233	$51.92	$51.90	$51.90
Purchase #6	$245.89	11.737%	$274.7501	$274.75	$274.75	$274.80
Purchase #7	$38.51	4.444%	$40.2214	$40.22	$40.20	$40.20
7 purchase totals =	$914.88		$998.6579	$998.65	$998.60	$998.60