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	$89.97	7.255%	$96.4973	$96.50	$96.50	$96.50
Purchase #2	$221.68	12.776%	$250.0018	$250.00	$250.00	$250.00
Purchase #3	$119.98	12.374%	$134.8263	$134.83	$134.85	$134.80
Purchase #4	$112.37	13.677%	$127.7388	$127.74	$127.75	$127.70
Purchase #5	$155.66	12.583%	$175.2467	$175.25	$175.25	$175.20
Purchase #6	$132.49	13.420%	$150.2702	$150.27	$150.25	$150.30
Purchase #7	$178.92	6.129%	$189.886	$189.89	$189.90	$189.90
7 purchase totals =	$1,011.07		$1,124.4671	$1,124.48	$1,124.50	$1,124.40