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	$89.60	9.874%	$98.4471	$98.45	$98.45	$98.40
Purchase #2	$36.72	9.269%	$40.1236	$40.12	$40.10	$40.10
Purchase #3	$227.35	12.597%	$255.9893	$255.99	$256.00	$256.00
Purchase #4	$183.41	11.124%	$203.8125	$203.81	$203.80	$203.80
Purchase #5	$230.34	12.850%	$259.9387	$259.94	$259.95	$259.90
Purchase #6	$118.83	10.775%	$131.6339	$131.63	$131.65	$131.60
Purchase #7	$87.71	13.820%	$99.8315	$99.83	$99.85	$99.80
7 purchase totals =	$973.96		$1,089.7766	$1,089.77	$1,089.80	$1,089.60