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	$95.70	7.391%	$102.7732	$102.77	$102.75	$102.80
Purchase #2	$140.65	3.175%	$145.1156	$145.12	$145.10	$145.10
Purchase #3	$31.78	4.155%	$33.1005	$33.10	$33.10	$33.10
Purchase #4	$104.51	11.255%	$116.2726	$116.27	$116.25	$116.30
Purchase #5	$74.70	4.481%	$78.0473	$78.05	$78.05	$78.00
Purchase #6	$141.39	10.241%	$155.8697	$155.87	$155.85	$155.90
Purchase #7	$118.97	7.278%	$127.6286	$127.63	$127.65	$127.60
7 purchase totals =	$707.70		$758.8075	$758.81	$758.75	$758.80