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	$108.66	12.600%	$122.3512	$122.35	$122.35	$122.40
Purchase #2	$35.45	8.795%	$38.5678	$38.57	$38.55	$38.60
Purchase #3	$183.37	9.597%	$200.968	$200.97	$200.95	$201.00
Purchase #4	$89.89	11.871%	$100.5608	$100.56	$100.55	$100.60
Purchase #5	$122.89	6.502%	$130.8803	$130.88	$130.90	$130.90
Purchase #6	$205.86	13.322%	$233.2847	$233.28	$233.30	$233.30
Purchase #7	$34.27	13.783%	$38.9934	$38.99	$39.00	$39.00
7 purchase totals =	$780.39		$865.6062	$865.60	$865.60	$865.80