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	$244.65	4.458%	$255.5565	$255.56	$255.55	$255.60
Purchase #2	$164.84	13.705%	$187.4313	$187.43	$187.45	$187.40
Purchase #3	$125.31	8.203%	$135.5892	$135.59	$135.60	$135.60
Purchase #4	$210.73	12.370%	$236.7973	$236.80	$236.80	$236.80
Purchase #5	$179.47	9.462%	$196.4515	$196.45	$196.45	$196.50
Purchase #6	$33.47	13.768%	$38.0781	$38.08	$38.10	$38.10
Purchase #7	$96.38	7.304%	$103.4196	$103.42	$103.40	$103.40
7 purchase totals =	$1,054.85		$1,153.3235	$1,153.33	$1,153.35	$1,153.40