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	$86.39	3.296%	$89.2374	$89.24	$89.25	$89.20
Purchase #2	$215.44	13.724%	$245.007	$245.01	$245.00	$245.00
Purchase #3	$246.26	5.830%	$260.617	$260.62	$260.60	$260.60
Purchase #4	$74.43	4.627%	$77.8739	$77.87	$77.85	$77.90
Purchase #5	$166.54	7.447%	$178.9422	$178.94	$178.95	$178.90
Purchase #6	$93.46	7.199%	$100.1882	$100.19	$100.20	$100.20
Purchase #7	$145.74	4.223%	$151.8946	$151.89	$151.90	$151.90
7 purchase totals =	$1,028.26		$1,103.7603	$1,103.76	$1,103.75	$1,103.70