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	$14.52	7.691%	$15.6367	$15.64	$15.65	$15.60
Purchase #2	$199.93	7.848%	$215.6205	$215.62	$215.60	$215.60
Purchase #3	$238.37	13.807%	$271.2817	$271.28	$271.30	$271.30
Purchase #4	$125.66	13.650%	$142.8126	$142.81	$142.80	$142.80
Purchase #5	$141.39	4.350%	$147.5405	$147.54	$147.55	$147.50
Purchase #6	$57.54	13.613%	$65.3729	$65.37	$65.35	$65.40
Purchase #7	$71.88	9.410%	$78.6439	$78.64	$78.65	$78.60
7 purchase totals =	$849.29		$936.9088	$936.90	$936.90	$936.80