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	$18.78	9.807%	$20.6218	$20.62	$20.60	$20.60
Purchase #2	$165.82	6.394%	$176.4225	$176.42	$176.40	$176.40
Purchase #3	$39.27	3.116%	$40.4937	$40.49	$40.50	$40.50
Purchase #4	$38.79	4.641%	$40.5902	$40.59	$40.60	$40.60
Purchase #5	$41.66	4.721%	$43.6268	$43.63	$43.65	$43.60
Purchase #6	$102.82	6.676%	$109.6843	$109.68	$109.70	$109.70
Purchase #7	$31.84	9.196%	$34.768	$34.77	$34.75	$34.80
7 purchase totals =	$438.98		$466.2073	$466.20	$466.20	$466.20