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	$249.52	6.794%	$266.4724	$266.47	$266.45	$266.50
Purchase #2	$171.85	11.502%	$191.6162	$191.62	$191.60	$191.60
Purchase #3	$195.88	9.798%	$215.0723	$215.07	$215.05	$215.10
Purchase #4	$104.59	4.235%	$109.0194	$109.02	$109.00	$109.00
Purchase #5	$50.44	7.500%	$54.223	$54.22	$54.20	$54.20
Purchase #6	$210.89	3.822%	$218.9502	$218.95	$218.95	$219.00
Purchase #7	$9.86	12.359%	$11.0786	$11.08	$11.10	$11.10
7 purchase totals =	$993.03		$1,066.4321	$1,066.43	$1,066.35	$1,066.50