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	$141.81	10.510%	$156.7142	$156.71	$156.70	$156.70
Purchase #2	$87.27	12.800%	$98.4406	$98.44	$98.45	$98.40
Purchase #3	$124.61	12.510%	$140.1987	$140.20	$140.20	$140.20
Purchase #4	$179.77	9.483%	$196.8176	$196.82	$196.80	$196.80
Purchase #5	$232.38	8.789%	$252.8039	$252.80	$252.80	$252.80
Purchase #6	$83.84	6.264%	$89.0917	$89.09	$89.10	$89.10
Purchase #7	$222.47	13.210%	$251.8583	$251.86	$251.85	$251.90
7 purchase totals =	$1,072.15		$1,185.9250	$1,185.92	$1,185.90	$1,185.90