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	$39.34	9.388%	$43.0332	$43.03	$43.05	$43.00
Purchase #2	$59.48	4.557%	$62.1905	$62.19	$62.20	$62.20
Purchase #3	$93.76	13.701%	$106.6061	$106.61	$106.60	$106.60
Purchase #4	$116.39	10.730%	$128.8786	$128.88	$128.90	$128.90
Purchase #5	$101.74	5.356%	$107.1892	$107.19	$107.20	$107.20
Purchase #6	$76.46	8.324%	$82.8245	$82.82	$82.80	$82.80
Purchase #7	$90.72	10.428%	$100.1803	$100.18	$100.20	$100.20
7 purchase totals =	$577.89		$630.9024	$630.90	$630.95	$630.90