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	$96.97	13.340%	$109.9058	$109.91	$109.90	$109.90
Purchase #2	$67.92	6.337%	$72.2241	$72.22	$72.20	$72.20
Purchase #3	$79.44	4.262%	$82.8257	$82.83	$82.85	$82.80
Purchase #4	$117.39	10.683%	$129.9308	$129.93	$129.95	$129.90
Purchase #5	$75.49	13.291%	$85.5234	$85.52	$85.50	$85.50
Purchase #6	$123.40	7.410%	$132.5439	$132.54	$132.55	$132.50
Purchase #7	$160.96	4.248%	$167.7976	$167.80	$167.80	$167.80
7 purchase totals =	$721.57		$780.7513	$780.75	$780.75	$780.60