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	$41.99	9.343%	$45.9131	$45.91	$45.90	$45.90
Purchase #2	$160.75	11.341%	$178.9807	$178.98	$179.00	$179.00
Purchase #3	$174.73	12.401%	$196.3983	$196.40	$196.40	$196.40
Purchase #4	$228.93	12.577%	$257.7225	$257.72	$257.70	$257.70
Purchase #5	$236.45	11.458%	$263.5424	$263.54	$263.55	$263.50
Purchase #6	$103.50	5.318%	$109.0041	$109.00	$109.00	$109.00
Purchase #7	$151.73	11.776%	$169.5977	$169.60	$169.60	$169.60
7 purchase totals =	$1,098.08		$1,221.1588	$1,221.15	$1,221.15	$1,221.10