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	$230.80	9.823%	$253.4715	$253.47	$253.45	$253.50
Purchase #2	$203.33	13.539%	$230.8588	$230.86	$230.85	$230.90
Purchase #3	$180.90	8.479%	$196.2385	$196.24	$196.25	$196.20
Purchase #4	$154.62	13.506%	$175.503	$175.50	$175.50	$175.50
Purchase #5	$231.68	10.670%	$256.4003	$256.40	$256.40	$256.40
Purchase #6	$157.46	5.794%	$166.5832	$166.58	$166.60	$166.60
Purchase #7	$90.97	8.382%	$98.5951	$98.60	$98.60	$98.60
7 purchase totals =	$1,249.76		$1,377.6504	$1,377.65	$1,377.65	$1,377.70