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	$121.46	6.145%	$128.9237	$128.92	$128.90	$128.90
Purchase #2	$30.83	5.221%	$32.4396	$32.44	$32.45	$32.40
Purchase #3	$27.50	3.175%	$28.3731	$28.37	$28.35	$28.40
Purchase #4	$128.89	7.747%	$138.8751	$138.88	$138.90	$138.90
Purchase #5	$127.79	7.830%	$137.796	$137.80	$137.80	$137.80
Purchase #6	$45.99	11.728%	$51.3837	$51.38	$51.40	$51.40
Purchase #7	$205.30	10.794%	$227.4601	$227.46	$227.45	$227.50
7 purchase totals =	$687.76		$745.2513	$745.25	$745.25	$745.30