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	$54.42	3.500%	$56.3247	$56.32	$56.30	$56.30
Purchase #2	$212.46	12.324%	$238.6436	$238.64	$238.65	$238.60
Purchase #3	$196.31	10.624%	$217.166	$217.17	$217.15	$217.20
Purchase #4	$48.85	10.256%	$53.8601	$53.86	$53.85	$53.90
Purchase #5	$234.57	9.294%	$256.3709	$256.37	$256.35	$256.40
Purchase #6	$125.94	3.144%	$129.8996	$129.90	$129.90	$129.90
Purchase #7	$113.84	9.461%	$124.6104	$124.61	$124.60	$124.60
7 purchase totals =	$986.39		$1,076.8753	$1,076.87	$1,076.80	$1,076.90