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	$244.55	6.750%	$261.0571	$261.06	$261.05	$261.10
Purchase #2	$160.29	13.299%	$181.607	$181.61	$181.60	$181.60
Purchase #3	$49.49	12.367%	$55.6104	$55.61	$55.60	$55.60
Purchase #4	$99.89	13.828%	$113.7028	$113.70	$113.70	$113.70
Purchase #5	$176.88	7.205%	$189.6242	$189.62	$189.60	$189.60
Purchase #6	$107.64	11.111%	$119.5999	$119.60	$119.60	$119.60
Purchase #7	$130.54	5.457%	$137.6636	$137.66	$137.65	$137.70
7 purchase totals =	$969.28		$1,058.8650	$1,058.86	$1,058.80	$1,058.90