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	$115.46	13.529%	$131.0806	$131.08	$131.10	$131.10
Purchase #2	$248.91	3.442%	$257.4775	$257.48	$257.50	$257.50
Purchase #3	$241.26	12.490%	$271.3934	$271.39	$271.40	$271.40
Purchase #4	$73.96	6.640%	$78.8709	$78.87	$78.85	$78.90
Purchase #5	$72.86	6.102%	$77.3059	$77.31	$77.30	$77.30
Purchase #6	$149.90	4.353%	$156.4251	$156.43	$156.45	$156.40
Purchase #7	$227.42	5.793%	$240.5944	$240.59	$240.60	$240.60
7 purchase totals =	$1,129.77		$1,213.1478	$1,213.15	$1,213.20	$1,213.20