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	$167.86	12.317%	$188.5353	$188.54	$188.55	$188.50
Purchase #2	$140.66	12.652%	$158.4563	$158.46	$158.45	$158.50
Purchase #3	$176.68	3.269%	$182.4557	$182.46	$182.45	$182.50
Purchase #4	$79.55	12.440%	$89.446	$89.45	$89.45	$89.40
Purchase #5	$85.82	3.247%	$88.6066	$88.61	$88.60	$88.60
Purchase #6	$155.80	7.788%	$167.9337	$167.93	$167.95	$167.90
Purchase #7	$76.38	11.377%	$85.0698	$85.07	$85.05	$85.10
7 purchase totals =	$882.75		$960.5034	$960.52	$960.50	$960.50