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	$149.55	4.111%	$155.698	$155.70	$155.70	$155.70
Purchase #2	$53.48	4.326%	$55.7935	$55.79	$55.80	$55.80
Purchase #3	$138.62	4.300%	$144.5807	$144.58	$144.60	$144.60
Purchase #4	$198.80	7.362%	$213.4357	$213.44	$213.45	$213.40
Purchase #5	$128.70	13.617%	$146.2251	$146.23	$146.25	$146.20
Purchase #6	$117.61	8.715%	$127.8597	$127.86	$127.85	$127.90
Purchase #7	$112.88	4.223%	$117.6469	$117.65	$117.65	$117.60
7 purchase totals =	$899.64		$961.2396	$961.25	$961.30	$961.20