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	$122.68	4.796%	$128.5637	$128.56	$128.55	$128.60
Purchase #2	$173.33	5.342%	$182.5893	$182.59	$182.60	$182.60
Purchase #3	$67.89	9.806%	$74.5473	$74.55	$74.55	$74.50
Purchase #4	$169.41	11.822%	$189.4377	$189.44	$189.45	$189.40
Purchase #5	$157.61	6.600%	$168.0123	$168.01	$168.00	$168.00
Purchase #6	$30.41	11.127%	$33.7937	$33.79	$33.80	$33.80
Purchase #7	$80.99	3.532%	$83.8506	$83.85	$83.85	$83.90
7 purchase totals =	$802.32		$860.7946	$860.79	$860.80	$860.80