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	$89.59	6.575%	$95.4805	$95.48	$95.50	$95.50
Purchase #2	$139.78	5.139%	$146.9633	$146.96	$146.95	$147.00
Purchase #3	$29.50	9.778%	$32.3845	$32.38	$32.40	$32.40
Purchase #4	$219.43	9.373%	$239.9972	$240.00	$240.00	$240.00
Purchase #5	$73.65	11.571%	$82.172	$82.17	$82.15	$82.20
Purchase #6	$122.58	4.264%	$127.8068	$127.81	$127.80	$127.80
Purchase #7	$100.27	5.303%	$105.5873	$105.59	$105.60	$105.60
7 purchase totals =	$774.80		$830.3916	$830.39	$830.40	$830.50