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	$18.91	13.440%	$21.4515	$21.45	$21.45	$21.50
Purchase #2	$29.83	12.410%	$33.5319	$33.53	$33.55	$33.50
Purchase #3	$92.78	9.325%	$101.4317	$101.43	$101.45	$101.40
Purchase #4	$145.63	11.825%	$162.8507	$162.85	$162.85	$162.90
Purchase #5	$80.57	12.177%	$90.381	$90.38	$90.40	$90.40
Purchase #6	$249.61	8.495%	$270.8144	$270.81	$270.80	$270.80
Purchase #7	$166.35	10.560%	$183.9166	$183.92	$183.90	$183.90
7 purchase totals =	$783.68		$864.3778	$864.37	$864.40	$864.40