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	$100.92	10.297%	$111.3117	$111.31	$111.30	$111.30
Purchase #2	$238.72	8.394%	$258.7582	$258.76	$258.75	$258.80
Purchase #3	$97.56	10.202%	$107.5131	$107.51	$107.50	$107.50
Purchase #4	$51.56	3.550%	$53.3904	$53.39	$53.40	$53.40
Purchase #5	$159.95	9.181%	$174.635	$174.64	$174.65	$174.60
Purchase #6	$233.62	12.557%	$262.9557	$262.96	$262.95	$263.00
Purchase #7	$32.27	11.609%	$36.0162	$36.02	$36.00	$36.00
7 purchase totals =	$914.60		$1,004.5803	$1,004.59	$1,004.55	$1,004.60