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	$89.95	13.492%	$102.0861	$102.09	$102.10	$102.10
Purchase #2	$40.51	5.825%	$42.8697	$42.87	$42.85	$42.90
Purchase #3	$126.92	12.311%	$142.5451	$142.55	$142.55	$142.50
Purchase #4	$228.96	5.613%	$241.8115	$241.81	$241.80	$241.80
Purchase #5	$64.47	4.834%	$67.5865	$67.59	$67.60	$67.60
Purchase #6	$220.33	6.410%	$234.4532	$234.45	$234.45	$234.50
Purchase #7	$82.72	9.612%	$90.671	$90.67	$90.65	$90.70
7 purchase totals =	$853.86		$922.0231	$922.03	$922.00	$922.10