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	$226.46	3.539%	$234.4744	$234.47	$234.45	$234.50
Purchase #2	$108.63	13.254%	$123.0278	$123.03	$123.05	$123.00
Purchase #3	$21.84	6.589%	$23.279	$23.28	$23.30	$23.30
Purchase #4	$93.69	12.543%	$105.4415	$105.44	$105.45	$105.40
Purchase #5	$203.79	13.652%	$231.6114	$231.61	$231.60	$231.60
Purchase #6	$82.72	10.813%	$91.6645	$91.66	$91.65	$91.70
Purchase #7	$35.69	12.687%	$40.218	$40.22	$40.20	$40.20
7 purchase totals =	$772.82		$849.7166	$849.71	$849.70	$849.70