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	$13.78	8.670%	$14.9747	$14.97	$14.95	$15.00
Purchase #2	$57.82	5.330%	$60.9018	$60.90	$60.90	$60.90
Purchase #3	$70.52	10.708%	$78.0713	$78.07	$78.05	$78.10
Purchase #4	$59.44	9.359%	$65.003	$65.00	$65.00	$65.00
Purchase #5	$249.97	13.871%	$284.6433	$284.64	$284.65	$284.60
Purchase #6	$18.61	10.350%	$20.5361	$20.54	$20.55	$20.50
Purchase #7	$61.30	10.612%	$67.8052	$67.81	$67.80	$67.80
7 purchase totals =	$531.44		$591.9354	$591.93	$591.90	$591.90