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	$50.57	7.397%	$54.3107	$54.31	$54.30	$54.30
Purchase #2	$179.88	10.369%	$198.5318	$198.53	$198.55	$198.50
Purchase #3	$94.91	5.848%	$100.4603	$100.46	$100.45	$100.50
Purchase #4	$208.27	9.752%	$228.5805	$228.58	$228.60	$228.60
Purchase #5	$98.44	3.166%	$101.5566	$101.56	$101.55	$101.60
Purchase #6	$20.90	5.104%	$21.9667	$21.97	$21.95	$22.00
Purchase #7	$97.95	7.545%	$105.3403	$105.34	$105.35	$105.30
7 purchase totals =	$750.92		$810.7469	$810.75	$810.75	$810.80