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	$137.79	3.449%	$142.5424	$142.54	$142.55	$142.50
Purchase #2	$138.43	9.353%	$151.3774	$151.38	$151.40	$151.40
Purchase #3	$228.53	10.453%	$252.4182	$252.42	$252.40	$252.40
Purchase #4	$40.64	3.209%	$41.9441	$41.94	$41.95	$41.90
Purchase #5	$114.89	11.320%	$127.8955	$127.90	$127.90	$127.90
Purchase #6	$188.36	13.325%	$213.459	$213.46	$213.45	$213.50
Purchase #7	$131.64	9.690%	$144.3959	$144.40	$144.40	$144.40
7 purchase totals =	$980.28		$1,074.0325	$1,074.04	$1,074.05	$1,074.00