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	$79.92	13.715%	$90.881	$90.88	$90.90	$90.90
Purchase #2	$153.37	11.176%	$170.5106	$170.51	$170.50	$170.50
Purchase #3	$135.72	5.647%	$143.3841	$143.38	$143.40	$143.40
Purchase #4	$203.77	12.552%	$229.3472	$229.35	$229.35	$229.30
Purchase #5	$105.63	11.770%	$118.0627	$118.06	$118.05	$118.10
Purchase #6	$32.56	8.861%	$35.4451	$35.45	$35.45	$35.40
Purchase #7	$132.72	3.121%	$136.8622	$136.86	$136.85	$136.90
7 purchase totals =	$843.69		$924.4929	$924.49	$924.50	$924.50