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	$232.77	6.687%	$248.3353	$248.34	$248.35	$248.30
Purchase #2	$104.83	7.410%	$112.5979	$112.60	$112.60	$112.60
Purchase #3	$98.88	12.320%	$111.062	$111.06	$111.05	$111.10
Purchase #4	$129.39	8.689%	$140.6327	$140.63	$140.65	$140.60
Purchase #5	$35.39	8.665%	$38.4565	$38.46	$38.45	$38.50
Purchase #6	$178.31	9.602%	$195.4313	$195.43	$195.45	$195.40
Purchase #7	$11.85	9.211%	$12.9415	$12.94	$12.95	$12.90
7 purchase totals =	$791.42		$859.4572	$859.46	$859.50	$859.40