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	$142.51	12.256%	$159.976	$159.98	$160.00	$160.00
Purchase #2	$128.26	11.165%	$142.5802	$142.58	$142.60	$142.60
Purchase #3	$23.31	5.424%	$24.5743	$24.57	$24.55	$24.60
Purchase #4	$38.50	4.757%	$40.3314	$40.33	$40.35	$40.30
Purchase #5	$132.91	3.661%	$137.7758	$137.78	$137.80	$137.80
Purchase #6	$247.64	4.551%	$258.9101	$258.91	$258.90	$258.90
Purchase #7	$98.44	11.661%	$109.9191	$109.92	$109.90	$109.90
7 purchase totals =	$811.57		$874.0669	$874.07	$874.10	$874.10