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	$120.31	7.131%	$128.8893	$128.89	$128.90	$128.90
Purchase #2	$204.96	9.788%	$225.0215	$225.02	$225.00	$225.00
Purchase #3	$163.80	8.807%	$178.2259	$178.23	$178.25	$178.20
Purchase #4	$134.85	7.760%	$145.3144	$145.31	$145.30	$145.30
Purchase #5	$112.89	13.308%	$127.9134	$127.91	$127.90	$127.90
Purchase #6	$93.27	5.454%	$98.3569	$98.36	$98.35	$98.40
Purchase #7	$95.52	7.521%	$102.7041	$102.70	$102.70	$102.70
7 purchase totals =	$925.60		$1,006.4255	$1,006.42	$1,006.40	$1,006.40