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	$147.44	13.735%	$167.6909	$167.69	$167.70	$167.70
Purchase #2	$51.99	10.128%	$57.2555	$57.26	$57.25	$57.30
Purchase #3	$248.28	13.211%	$281.0803	$281.08	$281.10	$281.10
Purchase #4	$181.29	7.533%	$194.9466	$194.95	$194.95	$194.90
Purchase #5	$42.85	6.452%	$45.6147	$45.61	$45.60	$45.60
Purchase #6	$72.76	7.767%	$78.4113	$78.41	$78.40	$78.40
Purchase #7	$14.66	8.408%	$15.8926	$15.89	$15.90	$15.90
7 purchase totals =	$759.27		$840.8919	$840.89	$840.90	$840.90