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	$158.42	13.333%	$179.5421	$179.54	$179.55	$179.50
Purchase #2	$109.85	10.470%	$121.3513	$121.35	$121.35	$121.40
Purchase #3	$176.62	4.802%	$185.1013	$185.10	$185.10	$185.10
Purchase #4	$86.80	5.473%	$91.5506	$91.55	$91.55	$91.60
Purchase #5	$115.82	11.160%	$128.7455	$128.75	$128.75	$128.70
Purchase #6	$112.82	5.851%	$119.4211	$119.42	$119.40	$119.40
Purchase #7	$86.45	11.759%	$96.6157	$96.62	$96.60	$96.60
7 purchase totals =	$846.78		$922.3276	$922.33	$922.30	$922.30