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	$121.33	12.648%	$136.6758	$136.68	$136.70	$136.70
Purchase #2	$223.89	10.263%	$246.8678	$246.87	$246.85	$246.90
Purchase #3	$40.80	11.364%	$45.4365	$45.44	$45.45	$45.40
Purchase #4	$208.90	10.522%	$230.8805	$230.88	$230.90	$230.90
Purchase #5	$167.31	8.417%	$181.3925	$181.39	$181.40	$181.40
Purchase #6	$145.70	5.318%	$153.4483	$153.45	$153.45	$153.40
Purchase #7	$185.76	10.795%	$205.8128	$205.81	$205.80	$205.80
7 purchase totals =	$1,093.69		$1,200.5142	$1,200.52	$1,200.55	$1,200.50