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	$73.31	13.227%	$83.0067	$83.01	$83.00	$83.00
Purchase #2	$67.77	11.370%	$75.4754	$75.48	$75.50	$75.50
Purchase #3	$111.81	10.267%	$123.2895	$123.29	$123.30	$123.30
Purchase #4	$214.65	7.342%	$230.4096	$230.41	$230.40	$230.40
Purchase #5	$169.62	11.659%	$189.396	$189.40	$189.40	$189.40
Purchase #6	$24.59	3.387%	$25.4229	$25.42	$25.40	$25.40
Purchase #7	$100.52	3.319%	$103.8563	$103.86	$103.85	$103.90
7 purchase totals =	$762.27		$830.8564	$830.87	$830.85	$830.90