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	$249.33	12.366%	$280.1621	$280.16	$280.15	$280.20
Purchase #2	$135.67	8.744%	$147.533	$147.53	$147.55	$147.50
Purchase #3	$217.41	8.307%	$235.4702	$235.47	$235.45	$235.50
Purchase #4	$137.98	13.151%	$156.1257	$156.13	$156.15	$156.10
Purchase #5	$37.42	9.309%	$40.9034	$40.90	$40.90	$40.90
Purchase #6	$145.58	3.288%	$150.3667	$150.37	$150.35	$150.40
Purchase #7	$162.71	6.629%	$173.496	$173.50	$173.50	$173.50
7 purchase totals =	$1,086.10		$1,184.0571	$1,184.06	$1,184.05	$1,184.10