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	$150.39	9.303%	$164.3808	$164.38	$164.40	$164.40
Purchase #2	$59.74	11.226%	$66.4464	$66.45	$66.45	$66.40
Purchase #3	$240.63	6.698%	$256.7474	$256.75	$256.75	$256.70
Purchase #4	$52.53	7.548%	$56.495	$56.50	$56.50	$56.50
Purchase #5	$249.35	9.834%	$273.8711	$273.87	$273.85	$273.90
Purchase #6	$28.32	7.783%	$30.5241	$30.52	$30.50	$30.50
Purchase #7	$27.57	6.572%	$29.3819	$29.38	$29.40	$29.40
7 purchase totals =	$808.53		$877.8467	$877.85	$877.85	$877.80