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	$13.72	8.121%	$14.8342	$14.83	$14.85	$14.80
Purchase #2	$38.60	9.522%	$42.2755	$42.28	$42.30	$42.30
Purchase #3	$162.71	10.270%	$179.4203	$179.42	$179.40	$179.40
Purchase #4	$134.72	4.381%	$140.6221	$140.62	$140.60	$140.60
Purchase #5	$149.85	3.770%	$155.4993	$155.50	$155.50	$155.50
Purchase #6	$55.66	11.172%	$61.8783	$61.88	$61.90	$61.90
Purchase #7	$172.40	8.198%	$186.5334	$186.53	$186.55	$186.50
7 purchase totals =	$727.66		$781.0631	$781.06	$781.10	$781.00