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	$125.28	10.170%	$138.021	$138.02	$138.00	$138.00
Purchase #2	$211.55	13.422%	$239.9442	$239.94	$239.95	$239.90
Purchase #3	$101.97	7.783%	$109.9063	$109.91	$109.90	$109.90
Purchase #4	$64.53	12.641%	$72.6872	$72.69	$72.70	$72.70
Purchase #5	$35.62	9.105%	$38.8632	$38.86	$38.85	$38.90
Purchase #6	$164.53	13.825%	$187.2763	$187.28	$187.30	$187.30
Purchase #7	$35.90	5.505%	$37.8763	$37.88	$37.90	$37.90
7 purchase totals =	$739.38		$824.5745	$824.58	$824.60	$824.60