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	$139.59	13.418%	$158.3202	$158.32	$158.30	$158.30
Purchase #2	$154.54	7.614%	$166.3067	$166.31	$166.30	$166.30
Purchase #3	$63.94	12.665%	$72.038	$72.04	$72.05	$72.00
Purchase #4	$222.81	5.191%	$234.3761	$234.38	$234.40	$234.40
Purchase #5	$193.45	9.329%	$211.497	$211.50	$211.50	$211.50
Purchase #6	$153.89	10.285%	$169.7176	$169.72	$169.70	$169.70
Purchase #7	$26.62	11.108%	$29.5769	$29.58	$29.60	$29.60
7 purchase totals =	$954.84		$1,041.8325	$1,041.85	$1,041.85	$1,041.80